A report in Health Psychology found that people with advanced kidney cancer who wrote their thoughts and feelings about their personal experience with the cancer slept better and longer than people who just wrote about impersonal subjects like diet, exercise and sleep. The ones who felt better wrote for just 20 minutes a day. They even felt more enthusiastic about tackling daily activities.
My thoughts would be to write about any illness you have and see if you sleep better and longer, too. Again, the key seems be to writing about your personal experiences with your illness.