As the others mentioned, you will be amazed at how quickly your little one will bounce back. He should be himself by the afternoon.
When they come out of anesthesia, they're confused and groggy and usually thrashing/flailing/screaming. It's hard to see but it usually settles in a short while. Also, your son will be hungry since he won't have been allowed to have anything to drink since before midnight (usually). Bring his usual drink along and ask if it's OK to give it to him. It will probably help.
Also, if he's not allowed to drink after midnight, wake him up around 11:30 to give him something to drink (more than just water). That will help stick in his stomach and make him less starving in the morning.
Finally, as someone else said, make sure to get antibiotic ear drops and ask about after care (whether ear plugs are needed for showering/bathing, etc. - doctors vary on that one).
It is a quick and easy surgery. I'm sure he'll do well. Good luck and best wishes!