You do realize people don't usually use falling asleep as a method of ignoring other people right? You said yourself you get angry and yell and then further down say that he now lies when you notice he fell asleep. He probably lies because he doesn't want to get yelled at. A healthy 27 year old man does not fall asleep the way you described, so it's pretty clear that there is something medical going on. It's interesting to me that your first reaction was to find it annoying and not concerning. I'm not trying to be shitty, I just think maybe you should take a step back and try looking at this situation from a different mindset than the one you have been.

Or he's a heroin addict...which would explain everything, but I doubt that's the case.