Before people start imagining CO as being in the same league as, say, helium, the definitions of CO I have found describe it as just "slightly lighter than air." What this tells me is that it is easily wafted around by even small air currents, and that it can fill or collect in spaces other than being up against the ceiling. A car exhaust can fill up a gargage to deadly levels pretty quickly, and a boat cabin is usually a lot smaller than a garage. An earlier poster talked about CO wafting into their boat from the generator of a nearby boat. So "up" isn't always so "up" it seems. I would think if a current of air is wafting it about your head while you're asleep, you got problems no matter how far below the cabin overhead your head happens to be.
-- Edited by Marin on Monday 14th of February 2011 10:19:13 PM
-- Edited by Marin on Monday 14th of February 2011 10:19:13 PM