It sounds like a sleep disorder to me. Funnily enough we had a mild incidence of this last night, my husband had been drinking, not loads but enough that he was half pissed when he went to bed, and he slept really restless, arms flailing, muttering away in between the hog like snoring, and just as I was falling asleep his arm came crashing down on my head. I shoved him back over to his side of the bed, and just as I was falling asleep again, he whacked me on the head. At which point I sat up, and yelled in his ear, "do it again and I will slap you back"... at which point my vocals in his lughole woke him up enough for him to look at me blearily, and stomp off to the spare room. Which was great as I could sleep in peace.
So, going back to the Op, if the husband is depressed, and it is affecting his sleep patterns, he is possibly having bad dreams, and he really does need to see his GP or it wont get any better. In the meantime, if he wont get any help, or until he does, it may be better if they sleep in separate beds.
If this is the only time that he is "violent" and when awake is a perfectly normal and kind person, (which my husband is), then it isnt aimed at her. None of us can be responsible for our actions while we are asleep, but in a situation as dangerous as this, he really does have to seek some help or risk his marriage.