That's called the roller coaster of life, buddy. You were the happiest person on earth and loved life? You were like an angel. Now you want to kill yourself. Now you're like a fallen angel.
Our life represents the duality of good and evil, black and white. Every ounce of happiness you recieve, you will get an equal amount of sadness later. Everything has to balance out.
Life exists in a state of two extreme polar opposites co-existing. It manifests like that in every aspect of our life. Like how in the USA we have a two-party system, republicans and democrats. Duality manifests itself in our lives as war and conflict.
After we die, there is no longer duality, but nonduality. All conflict ends, and the roller coaster stops. After death, all things come into perfect balance, and no longer exists in a state of two opposite extremes. All things come to rest, and complete and perfect peace.
My advice is to achieve as much balance while living as possible. Go to a doctor, you sound bipolar. Get put on mood stabilzers. It's better to exist in a state of emotional stability than oscillating between extreme happy and extreme sad.
After death, there is perfect balance and harmony. But you don't have to die to achieve some level of harmony in your life. Strive to strike a balance, and do what it takes to stabilize your emotions. Go to a doctor, god damnit.