That's the word. According to someone who claims to have gotten a straight answer from Acumen, they're lost in a sort of limbo between dimensions until he can find them and bring them back. They never seem to remember their time away from the prison.
[Thoughtfully.] Someone also claimed that there are people who make it home during those periods and do remember their time away, but since only one person has brought it up and that was secondhand... I don't know how to feel about it yet. Saying something like that would be a good way to stir up dissent and hope when people seemed to be giving in.