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It depends on what sedation was used. If it was the reversible kind of sedation (the kind where he gets a shot for the x-rays and then a shot to wake him up) this is normal. Especially since they most likely had to manipulate his body while he was sedated into an uncomfortable position to get the films. After he is awake he may be uncomfortable from the positions he was in while asleep.
If they didn't give him anything for pain, I can give you a dose of aspirin if you know his weight. Often it takes 8 hours or more for all of the effects of sedation or anesthesia to wear off.