When I have no tolerance, smoking weed can make me extremely anxious, and it can sometimes make me feel like utter shit physically, like I'm going to die, although there are some other more positive psychedelic effects. When I have developed a tolerance, these side effects go away and the high changes pretty much like you've described and becomes very chill and relaxing - but new, different side effects come into play when I try to stop (agonizing withdrawal).
I know a lot of people who react like this. Almost all of them have abused weed heavily in the past, so I think that weed just eventually fucks your body up and you react differently to it. They are very cautious how much they smoke in a sesh, if they haven't been smoking regularly, whereas if I've been on her hard for a few days or so, I grow accustomed to it and I can smoke as much weed as humanly possible and be fine.