From the moment you wake, to the moment you fall into slumber, the one thing you can control is breath. How you breathe is tantamount to how you feel. How do you want to feel? Breath is life. Use it, wield it. It can lower your stress levels, treat insomnia, and prepare you for a difficult task or conversation. Try a simple box breathing technique (breath in for 4, hold for 4, breath out for 4, hold for 4, repeat), just the concentration alone can help get you out of cycle of mental negativity.