My horse jerks his head up when I take off his bridle...?

My horse suddenly has this problem of jerking his head up when I take off his bridle! I thought he might have had a sore mouth the first time he did it but it persisted even after i gave his mouth time to heal. We have had an equine dentist out and she says everything looks fine. The vet has looked at him several times sense this starting occurring. This wasn't that big of an issue until one day he threw up his head and I was thrown against a fence. I had severe bruises on my back, I couldn't bend over, and I couldn't pick up anything heavy for a couple of weeks. Now I'm almost scared to take off his bridle.... Please help.