How old are you?
when did you start having this problem
Do you have any medical condition?
is it frank (red) blood or altered blood?
I am 46 and this has been happening for the past month. I have type 2 Diabetes and take metaformin. I am a former smoker, I quit 8 years ago.
The blood is dark red
Dental issues like teeth/gum disorders and bleeding disorders are the commonest cause of drooling blood at sleep.
dark red blood means altered blood less than 2 hours of exposure, meaning it happens in the early morning hours during REM sleep.
Please you need to get a dental consult as well as bl;ood tests to check the clotting mechanism.
If you are not on blood thinners, and it is not coming from the nose (you would notice). That is the best thing to do.
Other causes like hematemesis (vomiting blood) would not occur only at sleep