What Causes Severe Fatigue And And Excessive Daytime Sleepiness?

I have recently (this week) become extremely fatigued. I mean, I am falling asleep, sitting up while people are talking to me during the day at work. I am getting enough sleep at night and feel like I am sleeping well. I have tried drinking caffeine (which I don t normally do) to help but that doesn t seem to make a difference. It is not narcoleptic - I am able to pull myself out of falling completely asleep but it s a struggle to listen to people talk to me. Some changes in the past 3 weeks: I just moved from SD to CO, started a new job, moved in with my boyfriend and we have two dogs that are getting familiar with each other so all of that is pretty stressful. Also, my mattress is killing my back so I have been sleeping on the couch so I can walk in the morning because if I sleep on the bed my back almost cripples my ability to move. I can t be this exhausted. I need to feel rested. What is causing this???? Is it the altitude? I don t feel short of breath. I don t know but I just want to collapse and sleep immediately. I don t think it is low iron, I just had that checked and I have Hasimotos disease and I just had my thyroid check a short time ago and it was fine.