I do 45 minutes of intense cardio at the gym four or five days a week. It doesn't work for me. Which is to say, it does all sorts of wonderful things to my general sense of well-being, but does not cure my insomnia.
Have you tried meditation and mindfulness? Curious if clearing your mind and relaxation techniques would allow you to combat the anxiety of being worried of not falling asleep? If not, why haven't you tried it?