Is It Normal To Have Wild Behavior During Sleep?

My partner is a violent sleeper. He has hit me on numerous occasions, but mostly this is the result of his limbs flailing wildly. He is never otherwise violent whatsoever. A couple of nights ago he sat up in bed, with his eyes open, and hit me in the face. This time he used his full force and seemed very determined. He lay back down and carried on sleeping as if it had never occurred. He woke up to me crying, he was confused but caring towards me. I had to explain the situation to him, he had no recollection of the event. Is this behaviour at all natural and should I be worried for my safety or his mental health?