Generally the american military won't allow enlistment of people who might do strange things at strange times. Epilipsy might reoccur during stress. Who knows what could bring on an attack of Bipolar. if you have ever taken certain mind altering drugs, you are permanently disqualified. Physical injuries are different. a captain commanding an infantry company in Iraq lost a lower leg to a mine. They fitted him with a fake leg and he is going back as an infantry commander. but he had to proove that he could do the job.
You can proove that you can do the job with a physical injury, You can't proove that a mental thing will never reoccur.