Experiencing a sudden, uncontrollable shiver while asleep or immediately upon waking can be a confusing and unsettling experience. This phenomenon, known as nocturnal shivering, is the body’s attempt to rapidly generate heat through involuntary muscle contractions. While it often feels like a sign of illness, the causes are frequently tied to the normal workings of your body’s internal clock and your immediate environment. Understanding why your body loses heat and how it tries to warm itself up can shed light on this common nighttime disturbance.
The Role of Core Body Temperature Regulation During Sleep
The most common reason for nocturnal shivering relates directly to the body’s natural sleep cycle, which demands a lower internal temperature. The hypothalamus, a small region in the brain, acts as the body’s thermostat, setting the core temperature lower in the evening as part of the circadian rhythm. To achieve this lower set point, the body initiates peripheral vasodilation, where blood vessels in the extremities, such as the hands and feet, widen. This increased blood flow to the skin allows heat to dissipate more efficiently into the surrounding environment.
This heat loss causes the core body temperature to decrease, reaching its lowest point during deep, non-rapid eye movement (NREM) sleep. Shivering occurs if the ambient temperature is too cool relative to this new, lowered core set point. The body’s thermoregulatory system senses a discrepancy between the internal temperature and the surrounding air, triggering muscle contractions to restore the balance. The involuntary shaking is the fastest way for your body to produce heat and prevent the core temperature from dropping too far.
Environmental and Lifestyle Factors Causing Nocturnal Shivering
External factors in the bedroom environment can easily exacerbate the body’s natural cooling process, pushing it over the threshold into shivering. A bedroom temperature below the optimal range, generally considered to be 60 to 67 degrees Fahrenheit, can make the normal circadian temperature drop feel like a sudden chill. Insufficient or overly breathable bedding can also fail to provide the insulation needed to trap the heat being radiated away from the skin.
Certain lifestyle choices can also interfere with the body’s ability to maintain its thermal stability during the night. Consuming alcohol close to bedtime is a common culprit because it is a vasodilator, mimicking the body’s natural cooling process. Alcohol causes an initial rush of warmth followed by accelerated heat loss from the skin. This rapid heat dissipation later in the sleep cycle can lead to a significant drop in core temperature, triggering a shivering response.
A lack of metabolic fuel is another major factor, often caused by going to bed hungry or intense, late-night exercise. The intense heat generated during a vigorous workout is followed by an aggressive post-exercise cooling phase, which can overshoot the mark. If the body lacks adequate glucose reserves from fasting, it cannot generate the necessary heat through non-shivering thermogenesis, leaving shivering as the only remaining mechanism to correct the temperature imbalance. Dehydration also impairs the body’s ability to regulate its temperature effectively, as water is an essential component of the circulatory system that distributes heat.
When Nocturnal Shivering Signals a Medical Concern
While many instances of nocturnal shivering are harmless, their presence can occasionally signal an underlying medical condition requiring attention. The most recognized cause is the onset of a fever, where the body’s immune response releases pyrogens that raise the hypothalamic set point. Shivering, or “the chills,” is the body’s immediate, involuntary attempt to rapidly raise its temperature to meet this new, higher set point to fight off an infection.
Nocturnal hypoglycemia, or low blood sugar, is another common cause that can manifest as shivering, shaking, and cold sweats. This is particularly true for individuals with diabetes or those taking certain medications. When blood glucose drops below the level needed to fuel the brain, the body releases hormones like adrenaline, which can cause tremors and a feeling of being chilled. This is often accompanied by symptoms such as confusion, a rapid heart rate, or vivid nightmares.
Conditions affecting the basal metabolic rate, such as hypothyroidism, can also lead to chronic cold intolerance that is more noticeable at night. The thyroid gland is responsible for regulating metabolism, and an underactive gland slows this process, resulting in a lower-than-normal internal body temperature. If the shivering is persistent, occurs suddenly without a clear environmental cause, or is accompanied by severe symptoms like a high fever, unexplained weight loss, or extreme fatigue, consulting a healthcare professional is advisable.