From time to time I ask my clients to keep a journal, to keep track of their "good days" and "bad days" over a period of several months. For certain impairments, such a fibromyalgia, such a journal can be very helpful.
There is no listed impairment for fibromyalgia. So the case has to be decided at steps 4 and 5 of the sequential evaluation process. Furthermore, fibromyalgia does not fit well into the Social Security RFC analysis, because on a given day, a claimant may be able to do all the requirements of light work. The next day, however, the same claimant may be unable to get out of bed due to pain secondary to fibromyalgia.
The most likely route to a favorable decision for such a Social Security disability claim is that the administrative law judge determines that for several days each month you will be unable to work due to your fibromyalgia. As a result, the judge rightfully concludes that you are unable to maintain employment, and should be awarded Social Security disability benefits. You can help the judge make this determination by keeping a journal, so that you have an accurate record of how many "bad days" you have each month due to your fibromyalgia.
A journal can be helpful for claims based on other impairments, including chronic fatigue syndrome, chronic pain, depression and anxiety.