Seizures happen when nerve cells in the brain fire electrical signals in an abnormal, synchronized pattern. The causes range from temporary triggers like sleep deprivation and low blood sugar to permanent changes in brain structure from injuries, strokes, or genetic conditions. Understanding what drives seizures means looking at both what’s happening inside the brain electrically and what sets that process off in the first place.
What Happens in the Brain During a Seizure
Your brain runs on carefully balanced electrical activity. Neurons fire in coordinated patterns, with some cells exciting nearby neurons and others inhibiting them to keep things in check. A seizure occurs when that balance tips sharply toward excitation, and large groups of neurons begin firing together in intense, rhythmic bursts.
This doesn’t mean every neuron joins in. Early research in animal models found that only about one-third of recorded neurons actively participated in seizure patterns. The rest remained “passive.” At the start of a seizure, certain inhibitory cells (the brain’s braking system) actually fire intensely, trying to contain the spread. When that containment fails, the abnormal electrical activity can ripple outward, producing the physical symptoms people recognize: convulsions, staring spells, confusion, or loss of consciousness.
Anything that weakens the brain’s inhibitory signals or strengthens its excitatory ones can lower what neurologists call the “seizure threshold,” the point at which normal brain activity tips into a seizure. Many of the causes below work by shifting that threshold.
Sleep Deprivation and Stress
Sleep deprivation is one of the most commonly reported seizure triggers among people with epilepsy, and it’s well enough established that doctors sometimes use it deliberately to provoke abnormal brain activity during diagnostic testing. When you’re sleep-deprived, your brain produces more slow, synchronized delta waves, particularly in the frontal and parietal regions. That extra synchronization is exactly the kind of electrical environment that makes seizures more likely.
The underlying mechanism likely involves a reduction in a key inhibitory signaling system (the same one targeted by anti-anxiety medications and sleep aids). When that system weakens from lack of sleep, the brain’s ability to suppress runaway electrical activity drops. Emotional stress, while harder to measure in a lab, works through related pathways and is frequently cited as a trigger alongside missed sleep, illness, and skipped meals.
Low Blood Sugar and Electrolyte Problems
Your brain is extremely sensitive to the chemical environment of your blood. Two of the most common metabolic causes of seizures are low blood sugar (hypoglycemia) and low sodium (hyponatremia).
Sodium plays a direct role in how neurons generate electrical signals. When blood sodium drops below about 120 millimoles per liter (normal is roughly 135 to 145), seizures and impaired consciousness become serious risks. The speed of the drop matters as much as the number: a sudden plunge is far more dangerous than a gradual one. In documented cases, chronic low sodium levels have sometimes dipped below 100 without triggering seizures, while a rapid drop to a similar range caused repeated convulsions.
Low blood sugar starves the brain of its primary fuel source. Blood glucose below about 2.9 millimoles per liter (roughly 52 mg/dL) has been associated with seizure activity, particularly in newborns. In adults, hypoglycemia from diabetes medications, prolonged fasting, or excessive alcohol intake can produce the same result. Other electrolyte imbalances involving calcium and magnesium can also provoke seizures, though sodium and glucose are the most frequent culprits.
Alcohol and Drug Withdrawal
Alcohol withdrawal is one of the most dangerous and well-documented causes of seizures. When someone who has been drinking heavily for an extended period suddenly stops, the brain loses the depressant effect it had adapted to. The result is a rebound of overexcitation.
More than 90% of alcohol withdrawal seizures occur within 48 hours of the last drink, with the highest risk window falling between 6 and 48 hours. Seizures appearing later than 48 hours after stopping alcohol suggest something else is going on, such as a head injury or withdrawal from another substance taken alongside alcohol. Withdrawal from benzodiazepines (a class of anti-anxiety and sleep medications) follows a similar pattern, since these drugs act on the same inhibitory brain system that alcohol does.
Head Injuries
Traumatic brain injury is a significant cause of seizures, and the risk scales directly with how severe the injury was. For mild head injuries (brief loss of consciousness or short-term memory loss), the risk of developing epilepsy within five years is about 0.6%. For moderate injuries involving skull fractures or longer periods of unconsciousness, that rises to about 1.6% within five years. Severe injuries, especially those involving bleeding inside the skull or bruising of brain tissue, carry a five-year risk of roughly 11.5%.
The most extreme cases involve penetrating head injuries, where something breaks through the skull and the protective lining of the brain. In military studies of these injuries, more than 50% of patients eventually developed seizures. Seizures can appear within the first week after a head injury (early seizures) or months to years later (late seizures). Early seizures are more common in children, occurring in 30% to 35% of kids with severe head trauma compared to 10% to 15% of adults with similar injuries.
Flashing Lights and Photosensitivity
About 3% to 5% of people with epilepsy are photosensitive, meaning certain visual stimuli can trigger seizures. The critical factor is the frequency of flashing light. In a study of 170 people with photosensitive epilepsy, the peak response occurred at 16 flashes per second (16 Hz), where nearly 90% showed abnormal brain activity. Very slow flashes (3 Hz) triggered responses in only 3% of people, and very fast flashes (65 Hz) affected only 4%.
This is why seizure warnings accompany video games, concert lighting, and certain film sequences. The danger zone is roughly 8 to 25 flashes per second, with 16 Hz being the sweet spot for provoking a response in susceptible individuals.
Medications That Lower the Seizure Threshold
Several common medication classes can make seizures more likely, particularly in people who already have a seizure disorder. These include:
- Certain antipsychotic medications, both older and newer types, which are among the most well-known offenders
- Tricyclic antidepressants, an older class of antidepressants that can lower the seizure threshold and interfere with anti-seizure medications
- Tramadol, a pain reliever that has been directly linked to seizures even in people without a prior history
- Fluoroquinolone antibiotics, which can stimulate the central nervous system
- Amphetamine-based stimulants, which may reduce the effectiveness of anti-seizure drugs
- Lithium, a mood stabilizer used for bipolar disorder
If you have a history of seizures and are prescribed any new medication, it’s worth confirming that your provider is aware of that history. Many of these drugs are still used safely in people with seizure disorders when the benefits outweigh the risks, but dosing and monitoring may need adjustment.
Genetics and Family History
Some people are born with a lower seizure threshold because of inherited genetic changes. One of the most studied is the SCN1A gene, which provides instructions for building sodium channels in nerve cells. Hundreds of mutations in this single gene have been identified, and they cause a spectrum of seizure disorders ranging from mild febrile seizures in infants (fever-related convulsions that typically stop by age 5) to Dravet syndrome, a severe form of epilepsy that begins in infancy and is difficult to control.
The mutations work in different ways. Some change the shape of the sodium channel so it doesn’t open or close properly. Others reduce the number of working channels the brain produces. The result is the same: neurons become more excitable or less able to regulate their own firing. In younger people with epilepsy, a genetic cause is more commonly identified than in older adults, where accumulated brain injuries tend to dominate.
How Causes Differ by Age
The most likely explanation for a seizure shifts considerably depending on how old you are. In infants and young children, the leading causes are genetic conditions, febrile seizures (triggered by high fevers), low blood sugar, low sodium, infections affecting the brain, and oxygen deprivation at birth.
In older adults, the picture changes dramatically. Cerebrovascular diseases, primarily strokes, account for 30% to 50% of new-onset epilepsy in the elderly. Brain tumors cause 10% to 30%, head trauma accounts for another 10% to 20%, and neurodegenerative diseases like Alzheimer’s contribute 10% to 20%. Even with thorough testing, one-third to one-half of new seizure cases in older adults have no identifiable cause.
One Seizure vs. Epilepsy
Having a single seizure does not mean you have epilepsy. Many seizures are “provoked,” meaning they were caused by a specific, temporary condition: alcohol withdrawal, dangerously low sodium, a high fever in a child, or a medication reaction. Once that trigger is resolved, seizures may never return.
An epilepsy diagnosis generally requires either two or more unprovoked seizures occurring at least 24 hours apart, or one unprovoked seizure combined with evidence (from brain imaging or electrical recordings) that the risk of another seizure is high. The distinction matters because it determines whether long-term medication is recommended. Many people who experience a single provoked seizure never need ongoing treatment.