What does it mean when a guy shakes while making out? :L?

We're both 17. We were a little drunk and i was sitting on top of him making out and after a while i noticed that his shaking. Im SURE he wasn't nervous his done this nd more plenty of times. It was quite steamy and i stopped and told him to stop shaking once r twice and he Just idk kinda laughed it off and saying i cant.. ha. it was kinda funny cause it made vibrations but still really weird..? has this ever happened to anyone. when we were getting up i mentioned it again and he said he was just trying to hold me up, so i wouldn't fall of him. BUT i was defo not falling off!