Internal tremor, the sensation that your body is shaking, vibrating, or buzzing even though no movement is visible, is a well-documented medical phenomenon that researchers are still working to fully understand. It has been reported across a surprisingly wide range of conditions, from anxiety and Parkinson’s disease to long COVID, and it affects more people than most realize. A study across three neurological conditions found that roughly a third to over half of patients experienced the sensation, yet it remains poorly recognized in clinical practice and is often dismissed when patients bring it up.
What the Sensation Actually Feels Like
People who experience internal tremor describe it in remarkably consistent ways, even when their underlying conditions differ. One common description is of the whole body “humming,” as if sitting on a large speaker turned up to full volume. Others report their limbs bouncing or trembling in a way they can feel internally but that doesn’t always show up externally. The sensations can come and go unpredictably, sometimes lasting minutes and other times persisting for hours. They tend to happen at rest, often in the evening or at night, and they aren’t related to being cold or restless.
A qualitative study characterizing internal tremors found that patients frequently described “buzzing” or “vibrating” feelings in the trunk and limbs, with many noting that the sensation was impossible to convey to others because it had no outward sign.1PubMed Central. Characterisation of internal tremors and vibration symptoms That invisibility is a major source of frustration. People feel something genuinely distressing, and when doctors examine them, everything looks normal. The disconnect between what a person feels and what anyone else can observe is itself a defining characteristic of the symptom.
Anxiety and the Stress Response
For many people who feel like they’re shaking but aren’t, the culprit is the body’s stress response. When you’re anxious, your nervous system floods your body with norepinephrine (sometimes called noradrenaline), the chemical that primes you for action. That surge doesn’t just speed up your heart and tense your muscles. It can make your body feel like it’s vibrating or trembling from the inside, even when your hands are perfectly still.
Research on panic disorder has shown just how sensitive some people are to this chemical cascade. In a study comparing healthy volunteers with people who had panic attacks, administering a drug that boosts norepinephrine activity produced significantly greater increases in tremors, restlessness, anxiety, and other physical symptoms in the panic group. The rise in norepinephrine metabolites in the blood correlated with how much anxiety and nervousness people reported.2Archives of General Psychiatry. Noradrenergic Function in Panic Anxiety: Effects of Yohimbine in Healthy Subjects and Patients With Agoraphobia and Panic Disorder In other words, people prone to anxiety aren’t imagining the physical sensation. Their nervous system genuinely overreacts to stimulation, and “shaking that you can’t see” is one way that overreaction manifests.
This explains why so many people notice internal tremor during periods of high stress, after a panic attack, or even during seemingly calm moments when background anxiety is running high. The nervous system doesn’t always switch off cleanly. Residual sympathetic activity can linger for hours, producing that low-grade humming or buzzing feeling long after the acute stressor has passed.
Neurological Conditions and Internal Tremor
Internal tremor is especially well-documented in people with Parkinson’s disease, multiple sclerosis, and essential tremor. A study comparing patients across all three conditions found that roughly 33% of people with Parkinson’s, 36% of people with MS, and about 55% of people with essential tremor reported experiencing internal tremor.3PubMed. Internal tremor in Parkinson’s disease, multiple sclerosis, and essential tremor Those are not small numbers, yet the symptom rarely appears on standard screening questionnaires.
In Parkinson’s disease specifically, internal tremor occurs in an estimated 32 to 44% of patients, and for some people it is the very first symptom of the disease, appearing before the visible resting tremor that most associate with the condition.4PubMed Central. Internal tremor in people with Parkinson’s Disease: Demographic characteristics and comorbid symptoms The fact that an invisible tremor can precede visible symptoms makes it clinically relevant, not just a curiosity. If you’re someone in your 50s or 60s who has started feeling a persistent inner shaking alongside changes in movement, sleep, or sense of smell, mentioning it to a neurologist is worth doing.
The reason internal tremor shows up in these conditions likely relates to the same circuits that generate visible tremor. The brain’s motor control pathways, including structures deep in the brain that coordinate smooth movement, can begin firing in abnormal rhythmic patterns. Sometimes those signals are strong enough for you to feel but not strong enough to produce visible motion. Think of it as the electrical static before the signal becomes loud enough to move the dial.
Long COVID and Post-Viral Shaking Sensations
The COVID-19 pandemic brought internal tremor to wider attention. Many long COVID patients reported new-onset vibrating, buzzing, or shaking sensations that they had never experienced before their infection. A cross-sectional study of 423 people with long COVID found that 37% reported “internal tremors, or buzzing/vibration” as one of their symptoms.5PubMed Central. Internal tremors and vibrations in long COVID: a cross-sectional study That’s more than one in three, making it one of the more common neurological complaints in the long COVID population.
Researchers suspect the mechanism involves dysfunction of the autonomic nervous system, the branch that controls involuntary functions like heart rate, blood pressure, and digestion. A clinical report concluded that internal tremor in long COVID is likely a manifestation of postural orthostatic tachycardia syndrome (POTS) and small fiber neuropathy, possibly driven by a combination of low blood volume, reduced blood flow to the brain, overactive sympathetic nerves, neuropathic pain, and immune-cell overactivation.6PubMed Central. Internal Tremor in Long COVID May Be a Symptom of Dysautonomia and Small Fiber Neuropathy In plainer terms, the virus appears to damage or dysregulate the small nerve fibers and autonomic circuitry that keep the body’s background systems running smoothly, and the shaking feeling is one result of that dysregulation.
An exploratory neuroimaging study took a different angle, examining brain structures in long COVID patients with tremor-like symptoms and internal vibrations. The study identified structural abnormalities clustered around a specific brain interface involving the hypothalamus and connected brainstem pathways, supporting a model where a vulnerable brain circuit may contribute to the shaking sensations in a subgroup of severe long COVID patients. The authors were careful to note that this does not establish a single causal pathway or prove viral invasion of these structures.7medRxiv. The Mammillary Body-Fornix Gate in Long COVID An exploratory structural and diffusion MRI study of tremor-like symptoms, internal vibrations, and neuromuscular fatigue The research is early, but it suggests that internal tremor in long COVID may eventually have identifiable brain signatures.
Medications and Substance Withdrawal
Several commonly prescribed medications can produce tremor or internal shaking as a side effect. SSRIs (selective serotonin reuptake inhibitors), the most widely prescribed class of antidepressants, are one of the more frequent culprits. The mechanism isn’t fully understood, but one hypothesis is that SSRIs stimulate serotonin receptors in a brain structure called the inferior olive, which can overstimulate connected motor regions and produce tremor.8PubMed Central. Insights into Pathophysiology from Medication-induced Tremor For many people, this drug-induced tremor is subtle enough to feel but not see, placing it squarely in internal-tremor territory. Stimulants, bronchodilators, lithium, and certain anti-seizure medications can do the same thing through different pathways.
On the flip side, stopping certain substances can trigger shaking. Alcohol withdrawal is a classic example. Heavy drinkers who suddenly cut back or quit can experience tremors, anxiety, irritability, and agitation because the brain’s chemistry has adapted to the presence of alcohol and becomes excessively excitable once it’s removed.9PubMed Central. Introduction to alcohol withdrawal Caffeine withdrawal can produce a milder version of the same phenomenon. The common thread is a nervous system that was chemically held in one state and is now overcorrecting, creating sensations like internal trembling during the transition.
If you’ve recently started a new medication, changed a dose, or cut back on alcohol or caffeine and are now feeling an internal vibration you didn’t have before, the timing is a strong clue. This is worth raising with a prescribing doctor, because in many cases an adjustment solves the problem.
Hormonal Shifts and Perimenopause
Many women in their 40s and 50s report new-onset internal tremor during perimenopause and find it baffling because it doesn’t match any classic menopausal symptom they were warned about. Estrogen acts as a neuromodulator in the central nervous system, influencing serotonin, dopamine, and neuronal signaling. When estrogen levels swing during perimenopause, the brain systems that regulate mood, sleep, and sensory processing are directly affected. The result can include sensations of internal vibration, restlessness, or sudden “surges” of inner activation.
This connection is underrecognized partly because perimenopause is still heavily associated with hot flashes and mood changes in the public imagination, and an invisible tremor doesn’t fit neatly into that picture. But the nervous system and the hormonal system are deeply intertwined, and a major hormone fluctuation can absolutely produce sensory symptoms that feel neurological. Women who are experiencing internal tremor alongside sleep disruption, changes in their menstrual cycle, and temperature regulation problems may find that the hormonal link explains what felt like a mysterious neurological event. Hormone therapy has resolved the symptom for some, though formal trials specifically targeting internal tremor in perimenopause haven’t been conducted.
Functional Neurological Disorder
When all the standard tests come back normal and no clear medical cause is found, a diagnosis of functional neurological disorder (FND) sometimes enters the conversation. FND is not a wastebasket diagnosis for “we can’t find anything.” It’s an increasingly well-studied condition in which the brain produces real, often disabling symptoms through a problem with how it processes and integrates signals, rather than through structural damage you can see on a scan.
Recent neuroscience research frames FND as a disorder of the brain’s predictive machinery. Normally, the brain constantly generates predictions about what the body should feel and do, then updates those predictions when sensory feedback conflicts with them. In FND, the brain’s confidence in its own predictions can surge inappropriately, especially during periods of heightened arousal or stress. When that happens, the prediction overrides the corrective feedback, producing motor, sensory, or visceral symptoms that are genuine but have no structural cause.10PubMed. Precision dynamics of predictive coding in functional neurological disorder Internal tremor fits naturally into this framework: the brain predicts shaking and experiences shaking, even though the muscles aren’t actually producing it.
A review of motor dysfunction in FND found that patients tend to have difficulty predicting their own actions and detecting bodily cues, combined with heightened stress sensitivity and abnormally strong connections between emotion and motor systems.11PubMed. Mechanisms of motor dysfunction in functional neurological disorder: A narrative review This paints a picture of a nervous system that is both hyper-vigilant and poorly calibrated, a combination that easily generates phantom sensations. The good news about FND is that, because the problem is in signal processing rather than tissue damage, targeted rehabilitation and psychological therapy can improve symptoms over time.
Blood Sugar, Nutrient Deficiencies, and Other Triggers
Low blood sugar is a common and very fixable cause of feeling shaky. When glucose drops below normal levels, the body releases adrenaline to mobilize stored energy, and that adrenaline surge produces tremor, sweating, and a racing heart. For people with diabetes, these episodes are a recognized feature of hypoglycemia that helps signal when blood sugar needs attention.12PubMed Central. Symptoms of hypoglycaemia in people with diabetes But you don’t need to be diabetic to experience it. Skipping meals, exercising intensely without eating, or consuming large amounts of sugar followed by a crash can all push blood glucose low enough to trigger that shaky, buzzing feeling. The sensation is often internal, especially when glucose is dipping but hasn’t yet dropped dramatically.
Vitamin B12 deficiency is another overlooked contributor. B12 is essential for nerve function, and when levels are low, the nervous system can behave erratically. A case report documented a child with B12 deficiency who developed a combination of tremor and myoclonus involving the face, mouth, and arm, interestingly, the abnormal movements appeared after B12 treatment was started and resolved when it was stopped, illustrating how unpredictable the nervous system’s response to nutrient imbalances can be.13PubMed Central. Involuntary movements after correction of vitamin B12 deficiency: a video-case report In adults, B12 deficiency more commonly causes tingling, numbness, and balance problems, but internal tremor-like sensations have been reported as well. Vegans, older adults, and people on long-term acid-reducing medications are at higher risk of deficiency.
Vestibular disorders, which affect the inner ear and balance system, can also produce strange internal sensations. Vestibular migraine, one of the most common causes of recurrent vertigo in the general population, remains underdiagnosed partly because standard balance tests often come back normal. The diagnosis relies almost entirely on clinical symptoms, which can include a rocking, swaying, or vibrating sensation that overlaps with what many people call internal tremor. If your shaking feeling comes with dizziness, motion sensitivity, or headache, a vestibular component is worth exploring.
Why It’s Hard to Get Answers
One of the most frustrating aspects of internal tremor is how poorly it’s been studied compared to visible tremor. The standard neurological exam is designed to detect movement abnormalities that a clinician can observe and measure. Internal tremor, by definition, has no visible sign. There’s no standardized scale for it, no lab test, and until recently very few published studies focused on it as a distinct symptom. The research that exists has accelerated in the past few years, partly driven by long COVID making the symptom more visible to the medical community, but it’s still early.
This means that if you go to a doctor describing an internal shaking feeling and your physical exam is normal, you may be told nothing is wrong. That answer is technically incomplete. “We can’t find a visible cause” is not the same as “nothing is happening.” The sources covered in this article show that internal tremor is prevalent across multiple conditions, correlates with measurable nervous system dysfunction, and has plausible biological mechanisms behind it. It’s real. The medical system is just slow to catch up to symptoms it can’t easily observe.
When Internal Tremor Deserves Medical Attention
An occasional episode of feeling internally shaky after too much coffee, a stressful day, or a skipped meal is generally not worrying. The symptom becomes worth investigating when it’s persistent, progressive, or accompanied by other neurological symptoms like changes in coordination, balance problems, visible tremor, numbness, weakness, or cognitive changes. Any sudden-onset internal tremor that’s new and doesn’t have an obvious trigger warrants evaluation.
The practical challenge is knowing which specialist to see. A primary care physician is a reasonable starting point, but internal tremor can originate from the autonomic nervous system, the endocrine system, the vestibular system, or central motor pathways, so referrals may need to be targeted. If anxiety or stress is a major factor, a psychiatrist or psychologist may be the most helpful. If there are signs of autonomic dysfunction like lightheadedness on standing, abnormal sweating, or heart rate irregularities, an autonomic neurologist or cardiologist familiar with POTS can evaluate further. If visible tremor is developing alongside the internal sensation, a movement disorder specialist is the right call.
Keeping a symptom diary that tracks when the internal tremor occurs, how long it lasts, what makes it better or worse, and what other symptoms accompany it can be enormously useful. Patterns often emerge: the shaking may be worse before meals, worse after medication, worse during hormonal shifts, or worse during periods of poor sleep. Those patterns narrow the list of suspects and give your doctor something concrete to work with, since they can’t observe the symptom directly.
The Overlap Problem
One reason internal tremor is so tricky is that it sits at the intersection of multiple systems. Anxiety raises norepinephrine, but so does autonomic dysfunction from long COVID. SSRIs can cause tremor on their own, but they’re prescribed for the anxiety that also causes tremor. Perimenopause disrupts sleep, which amplifies anxiety, which worsens autonomic tone, which produces shaking. These feedback loops mean that for many people, there is no single cause. The shaking sensation is the final common pathway of several contributing factors stacking on top of each other.
This is why a strictly reductionist approach, finding the one cause and fixing it, sometimes fails. A person with perimenopausal hormone fluctuations, high stress, disrupted sleep, and an SSRI that slightly increases tremor likelihood may need to address several of those factors to get meaningful relief. Treating just the anxiety, or just adjusting the medication, may improve things partially but not completely. Recognizing that internal tremor is often a multi-system problem rather than a single-diagnosis problem can reframe expectations and guide a more comprehensive approach to management.