Storm Over Warlock by Andre Norton

Perhaps his status was that of a prisoner, but Shann was too tired to press for an explanation. He was content to be left alone in the unusual circular, but roofless, room of the structure to which they had brought him. There was a thick mat-like pallet in one corner, short for the length of his body, but softer than any bed he had rested on since he had left the Terran camp before the coming of the Throgs. Above him glimmered those patches of light symbolizing the lost stars. He blinked at them until they all ran together in bands like the jeweled coils on Warlockian bodies; then he slept -- dreamlessly.

The Terran awoke with all his senses alert; some silent alarm might have triggered that instant awareness of himself and his surroundings. There had been no change in the star pattern still overhead; no one had entered the round chamber. Shann rolled over on his mat bed, conscious that all his aches had vanished. Just as his mind was clearly active, so did his body also respond effortlessly to his demands. He was not aware of any hunger or thirst, though a considerable length of time must have passed since he had made his mysteriously contrived exit from the outer world.