Whenever I lie on a couch, face up, my dog lies on my belly. He does not like it when I get him off my belly, and he returns to his original position. I do not mind him doing so, but I want to understand why he does this.
Sounds like he thinks he owns you and that your belly is his rightful resting place. It’s the highest spot in the room; it puts him on top of you. He knows that when he is on your belly, you are completely vulnerable and in his control.
To prevent problems in the future and to clarify in your dog’s mind who is boss, I suggest you do not let him lie on your belly. Don’t let him onto the couch or bed with you without your permission. The highest spot in the room has the highest status in the dog’s mind. If he tries getting up, make him stay down.
When he has accepted your authority and learns to lie down beside the bed, after a while you might want to invite him up to snuggle beside you on the couch or bed. Not on top of you. Snuggling together will give you both a pleasant time. Making him ask your permission to come up will clarify who is boss.