I am a medium to heavy sleeper. I have slept through numerous earthquakes and I need to change my alarm clock about once every month in order for it to continue to be effective. I get used to the alarm after a while. I will continue sleeping if it gets bright in my room or uncomfortably cold or warm. I've done lots of things... using multiple alarms placed at different locations through the room, trying different wake up times (+/- 30 minutes). The best solution is to have another person whack me in the morning or throw water on me, although that doesn't always work either, because I am so tired sometimes that I fall asleep again if I don't instantly spring out of bed.
One thing I noticed... is that if I stay up very late (between 1 and 2 am) then I have little trouble getting up at 7am the next morning. I am exhausted for the rest of the day... but I am able to get up in the morning. Does anyone else have any experiences similar to this? Any explanation?