Sgraf. The same thing just happened to me last week. Come to find out the mirror is held by two small circular rods that holds it in place very tight.They act like a spring. I looks like it is designed that way for safety reasons. In case of an accident it pops out of its socket when it is hit instead of it jamming in your head.
The good news is that it is very easy to fix. As Dick mentions, you need to pop both lenses loose and using the tools that come with the car (small black bag in with spare tire) loosen the console that holds the mirrow , then remove the bracket that holds the mirrow. You will need to unscrew a large screw that holds the two rods that hold the mirrow. Sound complicated but once you open it up, it is a snap.

JB