As this quote suggests; Laughter is a cheap form of medicine and requires little effort to succeed in. I know that some people have difficulty finding a reason to laugh, or even smile about something, but if you don't try hard enough, you won't see the joy in anything. At one point, my happiness had faded out so much that I couldn't even reach for it anymore; I was that worn out and tired of everything.
Never in my life have I felt that way, and only recently have I seen the light, took a step back and hit the negativeness over the head with a great big mop and sent it back to where it came from. Being stuck in a negative and miserable state like that is never going to get you anywhere. If you don't try to be happy through your misery, and find something to be glad about, you'll never achieve it.
It is not as hard as it may seem to find humour in certain things, even the things that don't particularly need any amount of laughter at all. If you can laugh things off at times when you would likely do the complete opposite, you'll find just what you've been looking for, happiness and peace of mind. Try it, give a little laugh when you don't feel like it and you just might be surprised.