Physical and mental fatigue in post-COVID syndrome and their associations over time: A small-sample ESM-study to explore fatigue, quality of sleep and behaviours

Objective: Post-COVID syndrome leaves millions of people with severe fatigue, yet little is known about its nature in daily life. In this exploratory study, momentary associations between physical and mental fatigue, quality of sleep and behaviours over two weeks in patients with post-COVID syndrome were assessed. Method: Data on fatigue levels, quality of sleep and behaviours was collected for 14 consecutive days using the experience sampling method in ten ex-hospitalised patients with post-COVID syndrome. Results: Multilevel linear regression modelling showed strong associations between physical and mental fatigue (β = 0.61, p ≤0.001), significant both between and within individuals. Sleeping more hours at night was associated with less physical and mental fatigue the following day (β = −0.35, p = .001; β = −0.27, p = .008). Strenuous relaxation (B = 0.45, p ≤0.001; B = 0.28, p = .004) and social contacts (B = −0.33, p = .003; B = −0.22, p = .02) were associated with physical and mental fatigue at the same measurement point. Performing household chores decreased physical and mental fatigue (B = −0.29, p = .02; B = −0.30, p = .006) two hours later on the same day, whereas eating and drinking increased physical fatigue (B = 0.20, p = .05) two hours later on the same day. Conclusion: Physical fatigue and mental fatigue were strongly associated and revealed fluctuations in fatigue levels between individuals, which might suggest potentially different post-COVID subgroups. Indications for potential risk and beneficial behaviours for fatigue were found.