Disclaimer: Not a pro, didn't consult one either.
Can't recommend this as a one size fits all, but for me, discipline and cold logic helps. When emotions are unreliable and motivation is low, I bypass them to figure out reality checks
Pretty much brute forced my way out. Multiple times.
I basically had a set of "rules" - things I must do no matter how passive or unmotivated. An actual live kid depending on me helped - no way to pretend he isn't there.
And DAILY doses of love.
I got into growing plants. I find that giving/getting care both help. If there is no one who cares (or that you perceive) find someone/something to care about deeply.
Depression taught me a lot about sensitivity and creativity.
That's about it. Use logic to examine the feelings if they suck. Are they reasonable? Do things to feel better.
Yeah, I thought all that through too.
No idea if this helps, but thread was a result of someone saying "I'm broke, I can't afford to be depressed." and not as a joke.
So I did what I could to undermine sadness and sneak in anything that would make me happy.
Took discipline more than anything.
Make your rules for what to do when you are thinking clearly and you aren't allowed to change them when life sucks. That time is to put head down and one step after the other till through.
Instead, I found talking about specific problems and with people who were likely to have useful responses helped.
The worse it is, the narrower I make my scope. Bite sized pieces, strictly. Rest can suck, fixing this one starfish. At a time.