Hello, My Brother Has Serve Sleeping Walking And Hand Tremors.

Hello, my brother has serve sleeping walking and hand tremors. As a very young child he suffered from night terrors. His sleeping walking has gotten to the point where he leaves the house and usually he makes it home just fine.however this weekend, he disappeared. He was walking around, couldn't remember who he was, where he lived, or even where he was. He walked into a store asking for help and then wondered to a hotel where some police officers brought him home. He had no alcohol or drugs in his system. He was tested. What could be causing this?