The Conversation: "The stress-response neural systems of chronic fatigue syndrome (CFS) patients remain on high alert even when they sleep, signalling that it’s not safe to relax, researchers have found.
Researchers also discovered that reduced heart rate variability, or changes in heart beat timing, are the best predictors of cognitive disturbances, such as concentration difficulties commonly reported by CFS sufferers. This adds to the growing body of evidence linking autonomic nervous system imbalance to this disorder.
The findings could lead to new ways to improve cognitive difficulties in people with CFS, which remains a poorly understood condition."
ETS result in limited (reduced) heart rate variability and alters the ANS (sympathetic and parasympathetic balance). This article might provide some insight into the cases where ETS resulted in a variety of unwelcome and detrimental side-effects, including fatigue, altered cognitive function ('brain fog'), etc.
