First, I would like to take away the word "normal." Normal is really someone else’s standards of living imposed upon your life, and doesn’t mean that is what works for everyone.
I did some research and asked around in regards to this particular question. As it turns out, there is a sleeping disorder called sexsomnia. Sexsomnia is a parasomnia in which a person participates in sexual activities while sleeping. They will wake up in the morning with no recollection of their late-night friskiness.This disorder has a tendency to co-occur with one or several other issues. Does your partner take Ambien? I have been informed that some sexsomniacs report being on Ambien when these occurrences begin. Other considerations should include if your partner is sleep deprived or has another sleep disorder, such as sleep apnea. Sexsomnia also tends to present itself in individuals who have issues of substance or alcohol abuse. So, I ask you to look into your partner’s habits…is any of this familiar? Your partner could also participate in a sleep study where he is monitored while sleeping to observe his behavior.
I can empathize that this behavior could be problematic, so ask yourself whether it's problematic for you. You say that you don’t always mind your boyfriend's advances. Does that mean sometimes you find the behavior problematic? If so, be honest with yourself and your partner and attempt to troubleshoot solutions.
Because I lack the information of co-occurrence, you need to assess for yourself. Pay attention the next time or two this happens. Was he out drinking? Does he seem sleep deprived? Is your partner abusing a substance? From there, you can have a conversation about how to proceed. If substances are involved, that needs more and different attention. Clearly discuss with your partner that there are times when you can enjoy his spontaneity, and other times you find it disruptive. Be kind when informing him that you aren’t running away; just like traditional sex when both parties are awake, there will be times when you feel less than accommodating. It's fine if you would just prefer to be elsewhere on nights when he's likely to make nocturnal advances, but think about letting him know before you both turn in. It's best to let him down easy when he's still conscious.