Prozinc is less fragile than Lantus, if that makes you feel better! I get the impression that the "L's" have to be treated almost as carefully as nitroglycerin!
If you look at it and see little particle chunks floating in it, it may not be good any more. It should be cloudy, but no solids in the suspension. It can be "rolled" to make sure it's mixed well, but not shaken. I never dropped mine, but I was also using compounded PZI rather than Prozinc, so I don't know for sure exactly what Prozinc looks like.
Carl