the pain in your quads sounds a lot like how i felt the first week after i started working with a trainer who really worked my legs. and i usually walk/run and spin a good bit. but this worked my quads in a way that was not usual. i too could barely walk and had to ease myself down into a chair (toilet seat included) it was painful and embarrassing but i took it to be very normal for working very hard on muscles that i didn't work before. so i don't think i'd panic about the pain you were in. but like everyone else, i'd be very annoyed at an instructor who tried to adjust my tension for me, that is not something i've ever experienced in spinning.

hope your quads are feeling better real soon!