Back in 1999, researchers at the North Dakota State University published a paper in one of the world's most important journals, JAMA, on the effects of people with rheumatoid arthritis (RA) and asthma, being randomized to three sessions of 20 minutes of writing about the most stressful event of their lives (treatment group) or their plans for the day (control group).
It is somewhat surprising that the medical community seemed amazed that the treatment group who wrote about the most stressful event in their lives had significant marked improvements in their medical conditions, compared to the control group who had no change.
The RA group for example had a 28% improvement at four months follow up. That is comparable, for example, to the size of the benefit of the interferons or glatiramer in MS. This is one of the reasons I recommend people with autoimmune illness keep a diary or blog where they write about their emotional lives.
How much better a way of staying well this is than potentially toxic medications, particularly when used in combination with diet, exercise, sun exposure, etc.