It takes time, experience and perspective to stop reacting to everything that happens to you, good or bad. After awhile, we realize that we recover from most things, so it’s hard to just tell yourself it gets better until you see it in action. You have to learn by experiencing a few cycles of it.
In the meantime, the best thing you can do if you feel like crap is actually go help someone. Sometimes we’re too busy marinating in our own self pity that we find ourselves waiting for something great to happen. I find that causing a great outcome for someone who needs it actually turns into a positive for the self. Seems counterintuitive but it totally stokes the fires by creating a feeling of self worth while helping you realize you’re not alone in your suffering.
The other two are the tried and trues. Go for a walk in nature and breathe in the air. That and any form of exercise.
Those are my big three that help break the negative cycles.