Usually when I'm having days like this it means I need to take a step back and give myself a whole lot of love and self-care. For me, that usually means letting myself feel bad without beating myself up about it, watching something I enjoy, taking a bath, eating something delicious, etc. Basically, when I'm this tired, I let myself rest. Having PTSD is taxing, trying to work through it to get better is taxing, and it's okay to need - and take - a break.