HELP - Cat just home from having dental procedure

Just brought my cat home after dental cleaning and having an absessed tooth
pulled. The vet said her breathing would sound congested from her having a
tube down her throat. Indeed her breathing sounds like she has a very loud
congested purr (but there is no purr). The doctor didn't say how long this
would go on... anyone know?

She looks so tired, but she will not sleep. She was sent home with a
morphine type liquid med in syringes for pain, and I gave that to her 1-1/2
hours ago. I hoped that would make her comfortable and let her sleep, but
she just sits up, occasionally paces, and looks worn out. Shouldn't she be
tired and be out by now?

I've never had a cat go through this before, so if anyone can answer my
questions, I would appreciate it.