In November 2008, when he was just 6, William Moller had his first epileptic seizure, during a reading class at school. For about 20 seconds, he simply froze in place, as if someone had pressed a pause button. He could not respond to his teacher.

This is known as an absence seizure, and over the next year William, now 10, who lives with his family in Brooklyn, went from having one or two a day to suffering constant seizures. Not all were absence seizures; others were frightening tonic-clonics, also known as grand mals, during which he lost consciousness and convulsed.

The seizures often came while he was eating. As his body went rigid, William dropped his food and his eyes rolled back into their sockets. If he seized while standing, he suddenly crashed to the ground — in a corridor, in the driveway, on the stairs.

“It’s the scariest thing for any mother to hear that thump, and each time he would hit his head, so it only made things worse and worse,” said his mother, Elisa Moller, a pediatric nurse.