I've been going through this for about 16 months. Doctor's initially thought depression too but every single SSRI I have used does nothing, and they now admit I am probably not depressed.
I then thought it was adrenal fatigue after reading that article here. So I laid off heavy lifting for a few months. Didn't help at all.
From what I've been reading now, it looks like I have a mild, but still very disabling form of narcolepsy. Sleep study is scheduled but it will be a while. In the mean time I have started taking modafinil, which helps quite a bit.