He might be hibernating. Have you had a chance to feel how warm his underbelly is? If it is cold, you should warm him up. If you're going to warm him, make sure you don't put him under hot water or put him in front of a heater. You should stay calm. What you would have to do is, to keep your hedgie close to you and give him a blanket if he has one, or let him snuggle in a towel that came fresh from the dryer. If after about 10 - 15 mins of warming and he still isn't behaving normally, you should get him to a vet ASAP. If he has hibernated for about 72 hours, he may not be able to be revived, so act quick.