I have something that manifests itself as Chronic Fatigue. Doctors don't know the orgin. Some other symptoms I have are: joint pain, low body temperature and inability to get restful sleep. It's been about 5 years. My sister had fibromyalgia. I noticed 85% cocoa dark chocolate made a big difference one day and another. I doubled the dose and something miraculous happened. My cognitive function superseded that of when I was well. My energy also picked up. I had it first thing in the morning on an empty stomach with a glass of matcha green tea. I think it has an effect in three ways. It supplys calories without an insulin response due to the high fat and low sugar content. It increases blood flow via high flavonoid content and increases endothelial function. It has a stimulatory effect either on my central nervous system or via increases in serotonin. It's effects on my cognitive function is much more positive than something with a higher caffeine content such as coffee.