Seizure?

In 2003, my boyfriend was in an auto accident and received closed head injury to left temporal lobe. He was in a coma for 13 weeks. After he started physical rehab, he had some seizure activity, but that stopped 7 months after the accident. For the past year he has had several "episodes" in which he wakes up and is very aggressive and violent. Then just as soon as it comes on, it's over. He just lays down and goes back to sleep. When he wakes up again, he remembers nothing and is very upset over what has happened. His neurologist says that these "episodes" are seizures and has put him on Dilantin. What kind of seizures are is this and what else can be done to prevent them?