Have you tried mindfulness? There are lots of courses up and running now. The standard course is 8 x 2 hour sessions over 8 weeks, with practice in between. There is a book which sets out the basic approach and exercises for the 8 week course by Mark Williams and Danny Penman. You can buy it with a CD of guided meditations in the back. It's really helped me with my tendency to ruminate and angst over things, which affects my sleep badly when I'm in a bad patch.
If you can find & afford a course, I'd recommend it though - the group support and 'post match analysis' when you are trying out a new technique helps, as you see other people are struggling to get to grips with it too & that's quite reassuring.