Are these semen stains ??

In my experience the type of stain semen makes varies depending on age - when I was young they were the crusty sort and later if spilt on fabric tended to act like starch: nowadays it is more like a white dye and takes some getting rid of...

I suspect you believe someone might have performed anal sex on you while you slept. Do you really sleep that deeply or perhaps you were drugged? OR perhaps someone has watched you sleep while masturbating OR has used your bed while you weren't there???

Perhaps the stains are the result of something more innocent or perhaps you have had a nocturnal emission or two?
Certainly without other evidence or the benefit of information from a forensics laboratory it is pointless speculating and you could drive yourself daft by dwelling on it unless you really believe you were raped while you slept - in which case you need to get checked out by a medic to regain your confidence and prevent you inadvertantly doing harm to others...

You may be sleep eating. Semon is not green nor are your juices.
Sounds like oil to me.