It's funny how quickly my mood changes

This morning i was taking a walk outside. The sun was shining and the sky was so blue and mayday was playing in my ears and i began to skip. I felt perfectly content at that moment, just being able to take a nice walk on a lovely day while listening to music i love. In that moment i felt like everything was going to be okay, that everything will work itself out. All my worries seemed to dissolve and i experienced a moment of pure happiness. Yet now, i feel depressed about the state of my life. Im annoyed with myself. I feel like nothing will work out, none of my problems will solve itself and im doomed to live a life of misery. The rational part of me tells me that how my life will actually turn out will be like neither of these extremes, but rather something in the middle. But right now, i can't help but feel like shit.