Need help!

So last night I woke up to my partner choking me, he was completely asleep and this morning when I asked him if he remembered he didn’t and burst in to tears, he is terrified that he will do it again and hurt me, it happened once 2 years ago then last night,

I just want to know if anyone has felt with this or has any ideas what it could be or how I can help.

He’s the biggest softy I know wouldn’t hurt a fly so this has really scared him.