A seizure can happen to almost anyone under the right circumstances. Up to 10% of adults will experience at least one seizure in their lifetime, and only about 3% of those people will go on to be diagnosed with epilepsy. So if you just had your first seizure, the odds are actually in your favor that this may be a one-time event. But understanding why it happened matters, both for your peace of mind and for preventing another one.
The causes fall into two broad categories: provoked seizures, where something identifiable pushed your brain past its threshold, and unprovoked seizures, where no obvious trigger can be found. The distinction shapes everything that comes next, from your risk of recurrence to whether you need long-term treatment.
Provoked Seizures: Something Pushed Your Brain Over the Edge
Your brain runs on a careful balance of electrical activity. When something disrupts that balance acutely, it can trigger a seizure even in a brain that’s otherwise perfectly healthy. These are called provoked or acute symptomatic seizures, and they’re the most common explanation for a first-time event. Once the trigger is removed, the seizures typically stop.
The most common provoking causes include:
- Alcohol withdrawal. If you drink heavily and then stop or significantly cut back, the highest risk window for a seizure is 24 to 48 hours after your last drink. Alcohol suppresses brain activity over time, and when it’s suddenly removed, your brain rebounds into a hyperexcitable state. Binge drinking followed by a period of not drinking is a classic setup, and sleep loss from heavy drinking nights compounds the risk.
- Blood sugar drops. Seizures from low blood sugar typically occur when levels fall below 40 mg/dL. This is most common in people taking insulin or diabetes medications, but it can also happen after prolonged fasting or extreme physical exertion without eating.
- Low sodium levels. Sodium below 115 mEq/L is the typical seizure threshold, though if the drop happens rapidly, seizures can occur at higher levels. This can result from drinking excessive amounts of water, certain medications, or hormonal imbalances.
- Low calcium. Calcium levels between 5 and 6 mg/dL can provoke seizures. Thyroid surgery, vitamin D deficiency, and kidney disease are common causes of dangerous calcium drops.
- Drug use or withdrawal. Cocaine, amphetamines, and synthetic drugs can directly trigger seizures. Withdrawal from benzodiazepines or barbiturates is also a well-known cause, similar to alcohol withdrawal.
- Fever and infection. High fevers can lower the seizure threshold, especially in children. Infections that affect the brain directly, like meningitis or encephalitis, are a more serious cause that requires urgent treatment.
- Sleep deprivation. Going without sleep for extended periods is one of the most reliable seizure triggers, even in people who have never had one before. It frequently co-occurs with other triggers like alcohol use or stress.
Unprovoked Seizures: When No Obvious Trigger Exists
If no clear metabolic, toxic, or infectious cause is found, your seizure is classified as unprovoked. This is the category that raises the question of epilepsy, though a single unprovoked seizure does not mean you have it. The risk of a second seizure after a first unprovoked one is about 32% within the first year, 36% at two years, and 46% at five years. Epilepsy is only diagnosed after two or more unprovoked seizures, or after one seizure combined with brain imaging or EEG findings that suggest a high likelihood of recurrence.
Unprovoked seizures can stem from structural changes in the brain that have been quietly present for years or even decades before causing problems. These include:
- Old head injuries. Traumatic brain injury can create scar tissue that disrupts normal electrical patterns. Seizures from a head injury sometimes don’t appear until months or years later.
- Stroke. A stroke damages brain tissue, and the resulting scarring is one of the most common causes of new-onset seizures in older adults.
- Brain tumors. Both cancerous and benign tumors can irritate surrounding brain tissue enough to trigger seizures. A slow-growing tumor may cause a first seizure long before other symptoms appear.
- Abnormal blood vessel formations. Arteriovenous malformations and other vascular abnormalities can be present from birth and eventually cause seizures.
- Hippocampal sclerosis. Scarring in the part of the brain involved in memory is a common finding in temporal lobe epilepsy and may follow a childhood febrile seizure by many years.
- Developmental brain differences. Some people are born with subtle abnormalities in how their brain’s outer layer formed. These malformations of cortical development can cause seizures starting at any age.
In some cases, genetic factors play a role, particularly in generalized epilepsy syndromes that tend to run in families. And sometimes, despite thorough testing, no cause is ever identified.
What Happens During the Evaluation
After a first seizure, doctors typically run blood tests to check your glucose, sodium, calcium, kidney function, and liver function. If there’s any suspicion of drug use, a toxicology screen is added. Women of childbearing age get a pregnancy test. These basic labs can quickly identify or rule out the most common provoked causes.
An EEG (a test that records your brain’s electrical activity through sensors on your scalp) is considered essential after a first seizure. It’s most useful when done within 24 hours of the event, because abnormal electrical patterns are more likely to show up in that window. Specific patterns like spikes or sharp waves suggest a higher risk of recurrence. Normal results don’t guarantee you won’t have another seizure, but they’re reassuring.
Brain imaging, usually an MRI, looks for structural problems like tumors, signs of a prior stroke, scar tissue, or developmental abnormalities. In an emergency setting, a CT scan may be done first to quickly rule out bleeding or a large mass. If there’s concern about a brain infection, a lumbar puncture (spinal tap) may be performed. Heart monitoring is sometimes added when it’s unclear whether you actually had a seizure or fainted from a heart rhythm problem.
Was It Actually a Seizure?
Not every episode of shaking, passing out, or losing awareness is a seizure. Fainting (syncope) can cause brief jerking movements that look convincingly like a seizure, especially to bystanders. Cardiac arrhythmias can cause sudden loss of consciousness. And psychogenic nonepileptic seizures (PNES) are episodes that look like seizures but aren’t caused by abnormal electrical activity in the brain. They’re driven by psychological processes, often related to stress or trauma, and they’re surprisingly common. Up to 20-30% of people referred to epilepsy centers for uncontrolled seizures turn out to have PNES instead.
Some features can help distinguish true epileptic seizures from PNES. Epileptic seizures commonly involve biting the side of the tongue, turning blue (from disrupted breathing), and heavy labored breathing afterward. Recovery tends to be slow and confused. PNES episodes, by contrast, more often involve gradual onset, eyes closed from the start, side-to-side head movements, asynchronous limb movements, and relatively quick recovery of awareness afterward. Crying or speaking during the shaking phase points toward PNES, since epileptic seizures shut down the ability to produce purposeful speech. The definitive test is video EEG monitoring, which records both the episode itself and brain activity simultaneously.
Lifestyle Factors That Lower Your Threshold
Even if your seizure had a clear cause, certain lifestyle factors can make another one more likely by lowering your seizure threshold. Sleep deprivation is the single most potent and common trigger. Consistently getting fewer than six hours of sleep, working night shifts, or pulling all-nighters measurably increases risk.
Alcohol is a frequent co-factor, and its role is often misunderstood. Drinking doesn’t usually cause a seizure while you’re actively intoxicated. The danger comes afterward, as blood alcohol levels fall and withdrawal physiology kicks in. This is true even for people who don’t consider themselves heavy drinkers. A weekend of heavier-than-usual drinking followed by poor sleep is a textbook combination for a provoked seizure. For people with certain types of epilepsy, particularly generalized epilepsy, even moderate social drinking warrants caution.
Missed medications are another major factor for people already on antiseizure drugs. Skipping even a single dose can be enough to break through seizure control, especially with shorter-acting medications.
When a Seizure Becomes an Emergency
Most seizures end on their own within one to two minutes. A seizure becomes a medical emergency, called status epilepticus, when the active shaking phase of a convulsive seizure lasts longer than 5 minutes, or when seizures occur back to back without the person regaining consciousness between them. There’s also a nonconvulsive form, where someone remains in an altered, unresponsive state for longer than 10 minutes without visible shaking. Both require immediate emergency treatment because prolonged seizure activity can damage the brain.
A first-time seizure in someone with no seizure history also warrants an emergency room visit, even if it stops quickly. The goal is to identify any dangerous underlying cause, like a brain bleed, infection, or severely abnormal electrolytes, that needs treatment right away.