Take a minute, or two to read this excellent blog post at Creating Passionate Users. Kathy Sierra discusses how being around negative people can infect you with unhappiness. She points out the science of how people unconsciously mirror the behavior they are exposed to. That means if you hang with chronically unhappy people, you probably will become unhappy.
When I changed jobs last summer, I basically went through de-tox. It took me several months to adapt to a happy environment, where co-workers encouraged and helped each other. I hadn't realized how stressed out I had been before, until I had the mental space to relax.
The sad thing is that I can trace the whole negative environment to one or two people at the old job. These two were basically good people, who were desperately unhappy and afraid. Any change was viewed as a "problem", any creative thought was shot down. I think I fought against this tide for a while, but I got all caught up in it myself. Pretty soon the work day became a struggle for me -- I was unhappy. Of course there were other factors in my unhappiness, but I think the toxic people really crashed the work atmosphere.
Within a month of changing jobs, my father became seriously ill and then died. It was such a sad and tense period. But in looking back, I thank God I changed jobs when I did. I can't even imagine if I had to deal with Dad and have an unhappy workday. My new co-workers were very supportive and gave me the space I needed at that time.
Take a good look around at the unhappy places in your life. It may be time to evaluate the toxins you deal with, also check to make sure you aren't adding your own poison to the situation. Life is too short to be spent in negative spaces.