When thoughts rush into my head at night, I keep a note pad to make sure all the important tasks the next day won't be neglected. Mostly, I get eight hours though. Then I mentally sort through my life and try to make sense of it all. Pulling out the journal and writing gibberish. Sometimes I take a nap, but that rarely helps.
Walks are helpful.
I like to pack a bottle of water and a Walkman and walk. Connecting with people I know well on a deeper, more meaningful level. It still surprises me whenever I learn something new about someone I thought I knew really well. Striking up a conversation with a total stranger instantly makes me cheery too. I would say to spend some time thinking through what it is that makes you sad or stressed.