Two tricks I like.
One is to set a limit for number of losses in a day. Once you reach that limit you have to stop playing. So you might decide something like 5 losses. If you win 100 games in a row that's fine, but after your losses add up to 5 you have to stop.
The other trick is to pick a rating range. Let's say you're rated 1800, so maybe you pick 1750 to 1850. If you hit 1750 you have to stop for the day. If you hit 1850 you have to stop immediately after your next loss... so if you hit 1850 and win 10 games in a row that's great. But if you hit 1850 and lose your next game you have to stop for the day. The difference of this trick is by picking a rating range you're allowed to lose 100 games in a day (as long as you win 1 game after every loss your rating will stay near the same).
I have for the past few months been in a pattern where I'm going along, doing all right, when suddenly I, for no reason I can yet see, suddenly lose 100 - 200 points and then have to work my way back up to where I was, which is a difficult task.
But when I do get up to where I was, I surpass my highest rating score every time
It goes something like
1863 --> 1609
1880 --> 1770
1903 --> 1792
1912 --> 1825
1922 --> 1800 (where I am right now)
I seem to recover at some random moment, but then it takes me a few weeks to regain my position. I've tried practicing tactics, taking breaks from chess, getting better sleep, and even longer time controls, at which I lose slowly over a long period.
Any tips on how to recognize and prevent such demoralizing slumps would be (greatly) appreciated.