I'm going through this with my German Shepherd mix. She was completely fine with the vet and staff the first couple of times. I don't know if she had a bad experience with a nail trim when I wasn't back there with her or if it was when they did the fecal test on her and she didn't like that, but now she will NOT let any of them come near her. She growls, lunges, hackles go up. We tried the weekly vet visits for over a month where they give her treats and saw no improvement. The vet referred me to a trainer and a vet behaviorist. We tried medications (trazodone, gabapentin, clonidine, and even the dreaded acepromazine). They made her sleepy, but she still was alert and growled at the vet. I've been working with the behaviorist where she is having Bailey focus on treats in my hand while she touches her so eventually (hopefully) she will get to where she can be examined while focusing on me and the treats. Bailey has actually done very well with the behaviorist and her staff with this. I just CANNOT see her doing this for the vet and staff at all, plus it's hard to get the vet and staff to go along with everything exactly.
Just recently, Bailey also needed her vaccinations and heartworm test. The behaviorist wanted me to go ahead and have her sedated so that she could at least get these done since she was a little past due. She had me do a towel restraint on Bailey. I went in the exam room, knelt down next to Bailey, covered her eyes and head with a towel, the vet tech snuck in and gave her the sedation shot. Bailey was sedated and they were able to do blood work, heartworm test, vaccinations, and nail trim. Fortunately, she didn't have any major side effects from the sedation and was back to herself by the next morning. I could not believe this actually worked. I thought that Bailey would end up smelling the tech in there and go crazy, but she didn't.
I hated having to have her sedated, but I feel like I had tried everything. I hate seeing her react the way she does to the vet and staff. I hope this helps. You're definitely not alone!