pacing

my father has alzheimers and has recently started pacing. He can't sit for more than 2-3 minutes and then he paces back and forth for several minutes. This goes on for a couple hours at a time and is worse at night time. Anyone else experiencing this? How do you minimize it? I have tried redirecting him but that too seems to only last a couple minutes. When I ask him if there is something wrong he says he is nervous but never offers any clues as to what he is nervous about. Maybe he doesn't even know himself but I would like to be able to settle him down at night so we can both get much needed rest. Any advice would be appreciated, thanks.