Dr. David Bell, a fibro/CFS expert, has commented on this in the past. I wish I still had his quote and the source, but basically... he explained how a person could have mono symptoms and/or possibly CFS after a chemical exposure.
http://www.chemistryexplained.com/Ge-Hy/Heavy-Metal-Toxins.html
Any type of chemicals may be instrumental to the symptoms of FMS/CFS. If nothing else, the problem we have with Multiple Chemical Sensitivities alone would fall in this area. Ammonia and other cleaners can certainly cause health issues to those who are sensitive or work with these substances on a daily basis. A good idea would be to protect the skin and wear a mask (covering the nose and mouth) when using any type of chemical.