What does "knowingly asleep" mean? - given the panic described by most of the passengers how many people were knowingly asleep?
And, if you are knowingly, or even unknowingly asleep, does that mean that you can survive without oxygen?
I don't know if Big Burd's figures are right or not but I would be suprised if many people can sleep through an emergency descent. Presumably, if you find yourself next 'sleep and turn' in such circumstances you might do him the kindness of passing him an oxygen mask.
8,000 ft would be normal as the cabin is usually pressurised to this level. The air is breathable and it is a safe height. Clearly, this would not be appropriate over the Alps or Pyrenees!
I'm always amazed how many armchair experts we have! Keep it up chaps! - perhaps with the exception of 'slip and burn!'