According to the Gale Encyclopedia of Neurological Disorders, epilepsy is a chronic disorder of the nervous system that causes individuals to have periodic or recurring seizures. These seizures are triggered by "sudden episodes of abnormal electrical activity in the brain" and can involve a blend of abnormal body functions, both physically and emotionally. While these seizures can be prompted by a specific type of stimulus, such as flashing lights, or can be traced back to a cause, such as a brain injury or a genetic trauma at birth, many cases of epilepsy do not have an obvious stimulus or cause; this type of epilepsy is known as ideopathic epilepsy. 

• Fourth most common neurological disease
• 3.4 million people in the U.S. live with active epilepsy
• 65 million people in the world have epilepsy 
• Can affect any age group, but is most common in young children and older people
• 1 in 26 people will develop epilepsy at some point in their lives
• 150,000 new cases of epilepsy each year

• Stroke or transient ischemic attack (TIA)
• Dementia
• Traumatic brain injury
• Infections, such as brain abscess, meningitis, encephalitis, and HIV/AIDS
• Brain problems present at birth 
• Brain injury that occurs during or near birth
• Metabolism disorders present at birth 
• Brain tumor
• Abnormal blood vessels in the brain
• Other illness that damages or destroys brain tissue
• Seizure disorders that run in families

 Common causes from Medline Plus, Medical Encyclopedia entry - Epilepsy 

• Specific time of day or night 
• Sleep deprivation
• At times of fevers or other illnesses 
• Flashing bright lights or patterns
• Alcohol or drug use
• Stress 
• Associated with menstrual cycle or other hormonal changes 
• Not eating well
• Low blood sugar
• Specific foods or excess caffeine 
• Use of certain medications

Triggers from Epilepsy Foundation, Triggers of Seizures