Why Does My Dog Throw Up The Day After She Gets Groomed?

I was a pet groomer for almost five years, and I'm thinking that your dog is feeling a lot of stress from being at the groomer's shop.  It could be anything from the bathing, drying (do they use electric dryers, or towel only?), the strangers that are taking care of him, the noise of the other pets that are there also, etc.  At his age, he may have become very sensitive to having strangers doing all these services to him.  You may want to find a veteranarian whose office also offers grooming services, and specify that you have concerns about what has happened.  They may be able to groom him in a more calmer atmosphere.
 Also -- this is important -- you may want to stay with him the next time he has an appointment and check out how he is being treated during the time he's there.
Hope that helps you out a little!
Moe

First answer is exactly right. Dog is stressed out. Do they put a muzzle on it? Choke collar? Eight hours is a long time. I have a 120 lb. Newfoundland/Lab mix that was severly abused before I got him. Very strong but shy dog. After five years, will still flinch at sudden loud noises.But I am his trusted buddy, and as long as I am with him, or he is standing next to me, he is comfortable. Same noise can go off, no flinch.Point is, I am his security. Your dog is 13+ years. He is older,set in his ways, and you are his security blanket. Change it and who knows what can happen. Opt for mobile groomer in house with you present.