My cat is having spasms in his back and down to his hind legs after his vaccinations?

I took my cats to the vet today to have their annual vaccinations (bordetella, rabies, etc...) When we brought them home, my male cat started throwing up. I just thought that it was because of the stress of the vet. Well an hour into being home he started have real bad back and hind leg spasms. He couldnt sit in one place without one of his hind legs from spazzing right out from under him. He finally got some sleep but about an hour into his nap he woke up to the spasms again. Its breaking my heart. I'm not sure if the vet hit a nerve when giving him the shots or something went terribly wrong. I would really like to know if someone knows what is happening to my poor cat. He looks so miserable. SN: He is also loosing some clumps of hair. Not sure if that is just from stress.