Check his upper beak is still properly attached and that there is no discharge from the nasal tracks.
I would keep him caged up for a few days, as he probably has concussion. Makesure his diet is really good and as Diana suggests, you may wish to supplement his diet with vitamins or Spark, just to help.
His tail featehrs probably snapped when he slid down the window and landed. Keep a close eye on him, monitor his droppings and if anything seems out of place, get yourself and him of to the vets.
If God had intended man to fly, He would have given us wings. Instead He gave us Parrots.