A lot of us with fibromyalgia (FMS) and chronic fatigue syndrome (CFS or ME/CFS) have allergies, and allergic reactions can make our symptoms worse. Some doctors believe that we're more prone to food allergies, and allergies that change over time.
Benadryl (diphenhydramine) is a good drug to have on hand in case of a serious allergic reaction. For a severe reaction, especially if you're having trouble breathing, get immediate medical help.
Diphenhydramine also is the active ingredient in some over-the-counter (OTC) sleep aids, so it may help with insomnia. However, because it can make you tired, it's probably not the best choice for daily allergy treatment.
Be sure to talk to your doctor or pharmacist about possible negative interactions with other allergy medications you may be taking.