I don't know the answer to this. It could be a combination of the two I suppose. It would probably be worth talking over with your prescriber. Back when I was on antidepressants, when I would bring up a concern such as this to my pdoc, he would generally suggest I try taking my AD at a different time of day. (I don't recall that this made a whole lot of difference. But it may be something to try.)

In case you haven't already seen them here are links to 2 articles, from PC's archives, on how to overcome the overwhelming fatigue of depression:

5 Tips for Dealing with the Overwhelming Fatigue of Depression

5 More Tips for Dealing with the Overwhelming Fatigue of Depression