Last weekend I took my horse to the dentist. she was due (actually past due it turned out) to have her teeth "floated." What's really happening is the vet is using a pneumatic file to grind down sharp edges that form on their molars. Horses' teeth form sharp edges that can cause lots of problems, from not being able to chew their food well to creating sores inside their mouths.
After he's done, the vet gives the horse another shot. The antidote, if you will, to the powerful sedative that kept her happy while her teeth were being (loudly!) filed away.
The vet said most horses wake up faster.
This was after he put her halter back on her.
This was after I got her in the trailer. She was awake enough to step up into the trailer, but didn't quite have it in her to get that one back leg all the way in for a while.