the spring that hlds it in place has a small pin to locate the mirror in the place it's supposed to be held
there are also a few plastic prongs to hold it in the right orentation
what normally happens is that the pin holding the spring bends
you can unhook it with difficulty and realign it all with a new bit of metal, but it's a right royal pain in the arse
if you hold the mirror in the right place does it go back there? can you see if the pin has bent? is the plastic casing holding the pin in place bent?