Life is all ups and downs. I spend a lot of it in one extreme or the other. Chasing stability in happiness will generally be fruitless. Happiness is an emotion, just like any other; it's destined to come and go.

Protip: try your best to fill your time. Staring at the wall, laying in bed... I know how easy that is. I know how much it hurts in the long-term.

There's some great advice here, much of which I should take myself. But exercising, eating well, and finding a hobby that gives you a sense of accomplishment, are all great places to start.