Using somatic tools help me when I feel those waves off lowness. Rocking in my feet, head cradling, shaking arms, eye pointing etc theres lots of resources online to look at.
Acting as if or doing the opposite helps too. So one day this week I felt really rubbish and wanted to lie in bed feeding the gloominess. So instead I changed my sheets and bought a bunch of sunflowers and got on with my day. It's not always easy but I always feel on a day I've managed to use that tool that I've achieved something.
Behavioral activation like the 5 minute rule helps too. Getting on with a task for 5 minutes (Alexa or phone timer) and then seeing how I feel when those minutes are up, I might do fine more or I might stop there, but I'm self compassionate to myself and try to think well that's a good start, especially with how you are feeling right now.
Using inner voice as a third person 'right (my name) you are having a rough time/not feeling it today, you will be alright though..let's...' theres a good evidence base for this and if you cant do the inner voice then thinking about a hero 'what would Michelle Obama do if she was in this situation?'
Gratitude practice. And 'get to do' list. It's not barrgh I have to cook the dinner. Its I get to have food, I get to buy food that we will enjoy, I get to cook for my family because I have a family' etc.
The Happiness Trap by Russ Harris is one that I found has helped a lot with sitting with and accepting my feelings and being able to carry on with them there instead of feeling floored by them.