Before all my exercise intolerance and fatigue set in, I was fit with weight appropriate to height. When we eliminated other things, I had a sleep study - and whether I fit the profile or not - I have sleep apnea. It also has to do with the shape of the airway, tone of the muscles, and stuff like that. There are Dr's who conduct these sleep studies. Sounds like it'd be a good idea to have one done. They actually measure how many times an hour your breathing is delayed, if there's restless leg, and if you get into REM sleep.
If I don't use the CPAP machine, I can relate to the gasping for air thing.