Men's Group

Yes. It is.

The way to deal with this boundary question in real life is to have the conversation first. When you're NOT in bed.

"Is it OK to touch you sexually while you are sleeping?"

You can get a blanket yes or blanket no to that question pretty quickly. You might need to get more specific about what is and what is not OK touch.

If two people are in a relationship, it can be pre-negotiated that "sleep sex" or sexual touch while sleeping is a OK and is a normal and enjoyable part of that relationship.

If no such permission exists, it is sexual assault.

The boundary could also be like, "Well it's OK to try, but if I say no sometimes when you try, then please stop."

Or it could be, "No, please don't do that when I'm sleeping, not ever."

People seem to hate having those kinds of conversations, they'd rather just try stuff and see what the reaction is. I don't know what is wrong with asking before touching. It's not hard. I am a big fan of clear communication of boundaries and asking permission.