Years ago I had an online friend with ME/CFS who was still working full time. After a year of barely making it, she started feeling better physically. To her surprise, she got very depressed at that point - not when she was too sick to do anything but work or sleep. An RN friend explained to her that it takes energy to feel emotion, and that depression requires the least energy of any emotion. Therefore, when our energy levels begin to increase, all we are able to feel is depression. I still have mini-crashes (i.e. that last days or weeks, not several months or more) When I'm coming out of these I often get slammed with depression. It's a bit easier to take because I definitely know that it will pass, usually in a few days. I'm curious if anyone else experiences this or has another hypotheses for the phenomenon.