An Italian team evaluated the response to Oxygen-Ozone Autohaemotherapy (O2-O3-AHT) in a 100 patients with post-COVID fatigue found encouraging results. According to this paper, the researchers reported that treatment with O2-O3-AHT improved fatigue in all the patients, though with different degrees. About two fifths of the patients recovered almost fully. The effect lasted several months following completion of therapy.
The exact mechanism is not clear but it is thought to be related to the effect of Oxygen-Ozone therapy on endothelial dysfunction and the micro-thrombosis that is seen in sufferers of chronic fatigue in general (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7261521/).
The full paper can be accessed from this link: (https://www.europeanreview.org/wp/wp-content/uploads/5871-5875.pdf).