Slave Planet by Laurence M. Janifer

The room had no windows.

There was an air-conditioning duct, but Cadnan did not know what such a thing was, nor would he have understood without lengthy and tiresome explanations. He didn't know he needed air to live: he knew only that the room was dark and that he was alone, boxed in, frightened. He guessed that somewhere, in another such room, Dara was waiting, just as frightened as he was, and that guess made him feel worse.