You need to understand that there is a difference between someone: a) hitting you on purpose because they were upset with you/wanted to hit you AND b) someone being completely asleep/unconscious and swinging away because of a bad dream/nightmare
Someone can obviously be completely conscious while hitting/abusing you. On the other hand, someone can be complete Unconscious while hitting you, and thus, there was no intended harm at hand here.
Because of the only real relevant facts given in this case (he hit you, you have been together 8 years, and nothing like this has ever happened before), you should consider this an accident. It's very tough to diagnose. This man could truly have a sleeping problem that you have little knowledge of. His on and on talk about work that you mentioned he talks about while you're trying to sleep could actually be a symptom of a larger sleeping problem he has, and he/you could have little knowledge of the problem. I would love to have been given more information about the problem at hand. and how the problem was dealt with the next morning/day the incident happened. You need to compile everything that has happened in the relationship objectively, and think rationally about the situation. Most importantly, suggest he go to the doctor with you. At the minimum, he isn't diagnosed with anything and you realize that this is abuse (or you collect your thoughts and realize this is nothing more than a simple misunderstanding based on an unconscious action via an overload at work).
TL;DR: This man could be victim to a sleeping disorder. This man could also be abusive. Take the facts you have yourself objectively, and think about it all together. The truth will eventually come out, but you need to try to get him to a doctor to get him evaluated at a minimum. Talking to friends/family about the situation should also give you objectivity about the situation. My opinion: just an accident based on track record and info given. Get him a doctor's appointment, and use it as a growth experience together