Most people have times like that and it usually goes on for a bit, before it's over.
For times when there's too much to do, I prioritize, first. I look at just how important all these things really are, which ones will wait and which ones are critical. I look at whether I can delegate or do something differently. I decide what needs to be done first and then I do the best I can every day.
At bedtime, I let it all go. That day is over and I did the best I could. Tomorrow is tomorrow. I usually don't have trouble getting to sleep, but if I do, I usually imagine painting with watercolors, doing a color wash with a nice soothing aqua...
Eating a balanced diet and not skipping meals or overeating junk is important, too.
During those times, I also invest time every day in doing something that distresses me. When I worked long hours in an office, it used to really relax my mind to focus on gardening after work. Hobbies, reading or visiting with the chickens works, too. Or taking the dogs for a walk. It doesn't have to be a long stretch of time, it just needs to clear my head and let my body and mind reset.
Once in awhile, I get really stressed over something terrible. Then I do have to try very hard not to shut down. I prioritize then, too. I focus on doing just one thing at a time. When I lose focus, I make myself focus on just that one thing, until it's done. Then I pick the next thing to do.