Most people have it backward. When they are feeling down, they roll up their sleeves and get to work. They take their low moods very seriously and try to figure out and analyze what's wrong. They try to force themselves out of their low state, which tends to compound the problem rather than solve it.
When you observe peaceful, relaxed people, you find that when they are feeling good, they are very grateful. They understand that both positive and negative feelings come and go, and that there will come a time when they won't be feeling so good. To happy people, this is okay, it's the way of things. They accept the inevitability of passing feelings. So, when they are feeling depressed, angry, or stressed out, they relate to these feelings with the same openness and wisdom. Rather than fight their feelings and panic simply because they are feeling bad, they accept their feelings, knowing that this too, shall pass. Rather than stumbling and fighting against their negative feelings, they are graceful in their acceptance of them. This allows them to come gently and gracefully out of negative feeling states into more positive states of mind.
One of the happiest people I know is someone who also gets quite low from time to time. The difference, it seems, is that he has become quite comfortable with his low moods. It's almost as though he doesn't really care because he knows that, in due time, he will be happy again. To him, it's no big deal.
The next time you're feeling bad, rather than fight it, try to relax. See if, instead of panicking, you can be graceful and calm. Know that if you don't fight your negative feelings, if you are graceful, they will pass away just as surely as the sun sets in the evening.