My girl, Ms Kitty, had a dental procedure last year, the vet used ketamine and I was up all night crying. The cat acted as if she were blind and deaf and she didn't seem to know us. She was about 12 years old. I thought for sure that she was brain damaged. She did finally snap out of it but I won't ever let her have that again.
She had a procedure a few weeks ago where she had to be put under and she was alert and happy to see me within hours.