PEM is an exacerbation of some or all of an individual’s ME/CFS symptoms that occurs after physical or cognitive exertion and leads to a reduction in functional ability (Carruthers et al., 2003). As described by patients and supported by research, PEM is more than fatigue following a stressor. Patients may describe it as a post-exertional “crash,” “exhaustion,” “flare-up,” “collapse,” “debility,” or “setback.”2 PEM exacerbates a patient’s baseline symptoms and, in addition to fatigue and functional impairment (Peterson et al., 1994), may result in flu-like symptoms (e.g., sore throat, tender lymph nodes, feverishness) (VanNess et al., 2010); pain (e.g., headaches, generalized muscle/joint aches) (Meeus et al., 2014; Van Oosterwijck et al., 2010); cognitive dysfunction (e.g., difficulty with comprehension, impaired short-term memory, prolonged processing time)(LaManca et al., 1998; Ocon et al., 2012; VanNess et al., 2010); nausea/gastrointestinal discomfort; weakness/instability; lightheadedness/vertigo; sensory changes (e.g., tingling skin, increased sensitivity to noise) (VanNess et al., 2010); depression/anxiety; sleep disturbances (e.g., trouble falling or staying asleep, hypersomnia, unrefreshing sleep) (Davenport et al., 2011a); and difficulty recovering capacity after physical exertion (Davenport et al., 2011a,b). In some cases, patients experience new symptoms as part of the PEM response. [A patient quote follows]
