I just finished Chapter 4 of the Pickwick Papers, in which near end the fat boy who is always falling asleep is described. I seached for "neurology fat boy sleep" and found a site about sleep apnea that I think many members might find worth reading. Particularly if you know someone very obese who snores a lot, and feels tired all day.
http://www.mtsinai.org/pulmonary/Sleep/OSA.htm