I feel you. The dark places that it can take you can be scary and exhausting. I'm not religious, but one thing that helps me when I get in a dark thought space or I'm having a panic attack is telling myself "this too shall pass". It's kind of like my mantra. My emotions are all over the place and then having a husband that struggles with bi polar and depression, theres a lot of negative, horrible things that happen, but they always pass eventually.
You should be super proud of yourself for finding it in yourself to get whatever you got done, done. You got this. Can you find a way to take a day off work and everything to give yourself that break that you deserve?