I'm not sure that's true. I have sleep apnea and I've never used an alarm on a daily basis in my entire life. I've only been using a CPAP for about 2 years... but neither before nor after have I ever needed an alarm. I simply go to bed when my body is tired... and I sleep until I'm not tired. It usually means, for me, I sleep from about 9:30 p.m. - 5:00 a.m. and work 7-3...

Prior to using a CPAP I wouldn't expect sleep apnea folks to need an alarm because they'd already be waking up pretty frequently.. after the CPAP machine I'd expect it to be super easy to just go to sleep when tired and wake up when you wake up...

and before you say, "I have to be up at X o clock and if I slept until I was done sleeping I wouldn't be able to do it" .. I call hogwash... If you purposefully go to sleep early a few nights you can control your 'well rested' time until you get it to the right point.. and after using an alarm for a few weeks should be able to remove it and let your body wake you up... as long as you will listen to your body when you are tired.

I think this previous post talks about this type of sleep ( "free running sleep"?)

http://news.ycombinator.com/item?id=673726