I go through periods of time, sometimes a day or more, where I cannot stay awake. It took me 4 tries to type and send a 3-word email because I kept falling asleep, and this was in the morning and I was sitting up. My head is heavy and walking off-kilter when this happens and I have no choice but to sleep. What might cause this kind of thing. It's been recurring over the past few months. I do have sleep apnea that I do not use a c-pap for and dpression for which I am medicated and it is not affecting me profoundly in any other way at this time.