I have this problem as well 4 jobs in the last 4 years, but I am on disibility pension as well so that helps to ease the financial burden. I only work part time as I believe a full time job would see me in hospital. I think it is due to my bi-polar as well. I work with disabled people and take them on weekly outings so the work is a lot less stressful then the other jobs that I have had.
I suppose it depends on what work you can handle and whats in it for you when you are happy in a job you tend to stay longer.