Our current understanding of ME/CFS is that it is a complex, chronic, debilitating, physical disease characterized by post-exertional malaise, severe, and debilitating fatigue, cognitive problems, sleep dysfunction, pain, and immune, autonomic, neurological, endocrine, and gastrointestinal symptoms (
12). The severity of symptoms varies from day-to-day within the patient, and varies among patients. Severity of disease is graded from patients being mildly affected, through moderately affected, to the severely affected. The severely affected are either house- or bedbound, may be unable to move, speak or tolerate light (
13). Post-exertional malaise (PEM) is considered one of the key symptoms of ME/CFS and is defined as the exacerbation of the patient's symptoms following minimal physical or mental activity, occurring hours, days, or weeks after the triggering activity, and lasting for disproportionately long lengths of time (days, weeks, or months).