Buy something not too expensive with your poker winnings, something that can occupy your mind for a while, like a really good book.
When you're stuck in a down swing all you see is loss, you subconsciously expect to lose and whatever you think, you're unlikely to be playing your A game.
If you get the book, you see a tangible real world result from your hard work, not just numbers on a screen, and it'll also give you hours and hours of NOT THINKING ABOUT POKER!
That helped for me, although I still struggle with tilt, but no-one on the planet runs worse than me so that's to be expected.