It is also possible he may be having unrecognized or subtle seizures or that the underlying cause of his epilepsy is contributing to his slowing down. It might be worth discussing this with his physician. My 22 year old son has had epileptic seizures since he was 15, but only has them when is awakened from sleeping by any sudden noise such as the ringing of the telephone or doorbell, or if he wakes up and has to go the bathroom in the middle of the night. I have never known him to have any seizures except very late at night or in the morning hours between midnight and dawn. He takes 500 mg. of Dilantin per day.
Most epileptic seizures are more likely to occur during sleep or when the individual is drowsy.
The reason is not clear, but the brain is less able to inhibit seizures during those times. For the same reason, any EG in these individuals is more likely to be abnormal during sleep or during drowsiness. There are some forms of epilepsy, usually inherited ones, that only occur during sleep. There are also some forms that are more likely to occur when the individual is just waking up. This has to do with the underlying biochemical abnormality in the brain.