In February 2015, the Institute of Medicine (IOM) renamed chronic fatigue syndrome as systemic exertion intolerance disease (SEID), better reflecting the main symptom most patients experience. Up to 2.5 million Americans may have SEID, but the majority are undiagnosed.
SEID is more common in women, who typically display symptoms around the age of 33. The main symptoms are:
• Post-exertional malaise, following even minor physical or mental exertion
• Profound fatigue not alleviated by rest
• Sleep that is unrefreshing
• Cognitive impairment and/or dizziness or fainting when standing
According to the IOM, the cause is not known, but infections may cause symptoms. Many patients deal with SEID for years before being diagnosed. About one-quarter of them are house- or bedbound for a given period.