from Sleepfaring by Jim Horne.
Also apparently dolphins don't dream, because they only sleep with one half of their brain at a time so they can keep going up to the surface to breathe, and "the confusion in having half one's brain dreaming and the other half awake would be bewildering to say the least. Each side of the dolphine's brain can be sleep deprived separately, simply by waking the animal up as soon as this side sleeps, while letting the other side sleep normally." Which is like something out of Philip K Dick.
Also "hibernation is not a profound form of sleep, as is commonly thought, because hibernating mammals still have to arouse from hibernation in order to obtain some sleep."