Sorry, forgot something. I know it's stating the obvious, but don't touch him while he's sleeping. With my father, his episodes were sometimes preceded by external stimuli. We certainly grew to know to not add fuel to the fire.
My father acted out his bad dreams, and was actually dangerous to himself and the family. Please don't take this casually as you may be in harm's way.
The first thing I would want to know is if there is a sleep disorder that could be treated that would alleviate these symptoms. Some have REM behavior disorders. My father (in retrospect) had severe obstructive sleep apnea and I think at least some of his bad dreams may have been related to the panic a body feels when their breathing is blocked.
Secondly, it may be helpful to eliminate exposure to behaviors that could be harmful if replicated in dreams and acted out. No scary or violent movies or TV (even about vampires). I have to restrict what I watch because I will dream what I've seen except the characters will be people I know. Also, regularly getting adequate sleep and avoiding stimulants such as caffiene couldn't hurt.
Again, a sleep study may lend an understanding to how to best approach this. Keep in mind that if you aren't able to sleep well from being on alert for the next episode, your general well being will begin to deteriorate. The way you can help him is to suggest he take steps to understand and address this. From there, your safety should, without coercion, be his priority. Regardless of his response, make it yours.