In this study, 30 women with fibromyalgia were compared to 30 women without fibro. Tasks requiring attention were impaired as was the "working memory," and the cognitive dysfunction ("brain fog") worsened as the testing got harder. The authors conclude, "These findings point to disrupted working memory as a specific mechanism that is disrupted." Basically, short-term memory is problematic and gets worse with stress.
"Disruption of cognitive function in Fibromyalgia Syndrome." Bruce D. Dick, Michelle J. Verrier, K. Troy Harker, and Saifudin Rashiq, Pain, August 6, 2008.