Sudep’s name pretty much explains what it is: Someone with epilepsy — unprovoked seizures, which are electrical surges in the brain — dies, and there is no apparent cause. Often a person with epilepsy goes to bed and is found in the morning, unresponsive. In some cases, there is indirect evidence of a seizure, like urine on the sheets, bloodshot eyes or a severely bitten tongue, leading to the suggestion that preventing seizures as much as possible with medications could lower patients’ risks. But so much about the syndrome remains unknown.

Neurologists say sudden unexpected death in epilepsy is second to stroke as a cause of years of life lost because of a neurological disorder. Sudep kills an estimated 2,600 people a year in the United States — some neurologists say the real figure is almost certainly higher — or one in 1,000 people with epilepsy. For people whose seizures are not controlled with the medication, the fatality rate is one in 150.

Some three million Americans and 50 million people worldwide have epilepsy. About a third of Americans with epilepsy have uncontrolled seizures, said Dr. Daniel Friedman, an epilepsy researcher at New York University. That means about a million Americans could be at high risk of sudden death.

Ms. Pearson’s son was having at least 24 seizures a year despite anti-seizure medication. She could not bear to tell him about the sudden death risk. But he found out anyway three months later. He was meeting with an epilepsy support group meeting near their home in Galveston County in Texas and overheard people discussing it.

Ms. Pearson and her son were not alone in finding out about sudden death in epilepsy by accident. Despite the urging of professional organizations like the American Epilepsy Society and leading researchers to give patients the full picture, neurologists shy from a discussion of this phenomenon. The problem is that, at least for now, risk estimates are uncertain, and there are no proven ways to prevent it.