I have read a few stories about people getting attacked in their sleep, and I don't think it's very realistic.
Wild animals have very light sleep. Even my dog wakes up pretty much always when I just try to just get up from a chair while she is sleeping.
People back then were probably quite a bit more similar to animals, and they probably knew something could possibly kill them in their sleep if they didn't wake up, so I bet they would wake up if they heard something suspicious.
Even I myself wake up every time someone enters my room when I sleep, and I know why I woke up, so I think if something opens door to your cabin in the middle of forest, or gets really close to you it should be 100% chance you wake up (unless you have very poor hearing). Especially if you have seen e.g. a njerpez warrior, or a bear, the day before (or, a few days).
Also I think you should be also able to bar the door. It's not that hard to make something that allows you to prevent door from being opened from outside.
And for now the wake up messages are very general "You think you heard some rustle" or "You think you saw something move in the distance".
Considering, that I myself often know what I am woken up by, I think our character should also know it. Not always, but the closer the sound source is, and the more dangerous it feels to character, the highest chance there should be he knows.
So if you hear another human is close to you, and approaching you in your sleep, you should wake up and get message "You think you hear footsteps". If it's a bear, "You think you hear walking big animal". But if it's either far away, or just a squirrel/some bird, then it would make sense to not know what woke you up, because your mind doesn't put much attention to it.