I went to a sleep clinic about 6 years ago as I wasnt sleeping well and my wife said I stopped breathing. I arrived around 9 in the evening and was put in a room on my own. A nurse then strapped some wires to my chest, a heart monitor to my finger and a mask over my mouth and nose to monitor my breathing. Then I was left alone to go to sleep. Didnt have any problem going to sleep there, it was a quiet room.
Was woken up next morning around 7 and told to make an appointment for a couple of weeks for results. In my case I had sleep apnea, for every hour of sleep I stopped breathing 72 times! So basically I stopped breathing, gasped for breath, stopped breathing... Never got to REM sleep, which is why I felt so bad.
Sleep apnea does affect 'larger' people, but in my case I was told that even if I had the body of an olympic athlete it wouldn't help. I now sleep with a CPAP machine pumping air down my nose, forcing my windpipe to stay open - it has helped me a lot, although I still have problems every now and then, especially when I get a cold!