That's a hard question, not knowing any of what's got you down.
My usual method is to keep busy. If you're going to be miserable, you know that, and dwelling on it isn't going to get you anywhere, might as well make the time count. Some part of your brain'll be cranking away on the torment, but meanwhile things get sorted out. Clean things, organize whatever, finally deal with some long-procrastinated chores, solve pesky issues that melt away with a little foresight and elbow grease.
The redeeming power of hard work is an easy thing to suggest here. It doesn't have any of the follow-on affects that overdoing other self-care can have. Like, if your go-to move for crushing waves of sorrow is eating really well, it can work, but a couple of extra stones of weight comes with its own tangential issues.
Or, journaling for instance. Maybe it works for some folk, but I'd rather not get sucked into myself if I'm not fit company to be around.
What do you do? What did you do over the last hour since you posted?