Hope all is well with your kitty at the vet...sedating them is not uncommon but is not commonplace either. Generally everything is tried first before resorting to that..a vet should try with minimal restraint (sometimes less is more), E-collar, scruffing, etc. before resorting to sedation, but sometimes it needs to be done. Cats that are freaked out can also have what's called a cystocentesis reaction (due to a bladder stick) if they need to get urine...happens rarely but I've seen it once or twice, and they go into anaphylactic shock and can even die. It's much safer if the cat is calm for that (even with sedation).
Onlyfornow, I sure hope you aren't bleeding cats with a 20G (unless it's a tom) in it's carotid, or femoral artery for that matter! No wonder the cat is pissed :-)