Boyfriend falls asleep at rude times?

I love my boyfriend, but there's one thing he does that REALLY bugs me. I will be trying to talk to him and he will just stop replying and start snoring softly. So then I say, "you're falling asleep" and he gets all mad and goes "NO I'M NOT!!!" and then does the same thing again. He always says that he just doesn't have anything to say, but I'm not that stupid, because he only does it while he's laying down with his eyes closed. He also pretty much immediately falls asleep after orgasm, so there is never any chance of me getting any reciprocation. I understand that this one is not completely his fault, but I've told him a million times that it hurts my feelings. One time he fell asleep in the middle of giving me oral sex, which as you can probably understand, made me feel pretty shitty. I just don't get how he doesn't understand that he's being really rude when he does this. He just says "sorry" really nonchalantly every time I bring it up. I say "it's okay, just try not to do it" but he always does. I just want him to cut it out. It's just really unlike him to be such a jerk.