A vital practice in the art of being happy is appreciation. Appreciation can be very hard when you're feeling low or scared. That's the time to scale down. Look immediately around you. Is there anything there that you can see and admire.
Right now, I have a pink quartz crystal that's by my computer. It's so pretty. Just enjoying it's color and shape changes my vibration, coaxes it higher. I wonder what else has that power. I look and see the color of the sky, the bird at the feeder, and so many other small miracles. Appreciating the small things can change you. Let yourself do just that, and see if you don't feel just a little better. Gather small things around you that you like in preperation for those low moments. The act of taking care of yourself in this way will even help you appreciate yourself.