Unless you keep him under the right conditions (cooler, away from disturbances) he'll likely wake up on his own in a couple of weeks. If you want to keep him down, put him somewhere cooler in the house and just lightly mist his tank every day or two. I say cooler because when they bury themselves they get down to cooler, more stable temperatures.

To wake him up deliberately, give the tank a good soaking. He should be up in a couple of hours.