I've often considered unnatural/unwarranted fatigue after a dive to be significant of decompression stress (non-symptomatic DCI). Some believe this fatigue stems from excessive microbubbles occurring in the body... something that can happen very easily with fast tissues on shallow recreational dives; especially if there are saw-tooth profiles, faster ascents, limited stops and repetitive dives.
I have been reading, with interest, recently on the relationship between bubble formation and immune-system responses in the body. Some of those responses seem to link with other studies completed on endurance athletes, whose physical activities also trigger an immune response and brain chemistry changes - believed to result in significant fatigue and decreased vitality.
Microbubbles exist in all divers on ascent and, for a time, at the surface. They are measured with doppler ultrasound. However, they are not of sufficient size to cause diagnosable DCI symptoms, resolve themselves without immediate injury (although there is disccusion of long-term effects such as osteonecrosis and brain lesions) and do not require medical treatment.
The number of microbubbles occuring in the body (the 'bubble score') is known to be effected by ascent speed and the depth/duration of off-gassing (deco or 'safety') stops.
Nitrox reduces nitrogen absorption for a given dive profile (time and depth) compared to air. That, in itself, will decrease the propensity for bubbles, large or small.
Perhaps more importantly in this context, Nitrox also widens the off-gassing gradient upon ascent. It 'accelerates' decompression, compared to air. That helps reduce decompression stress... and may (I propose...) reduce the incidence of microbubbles throughout the body - alleviating otherwise unwarranted or unnatural fatigue post-dive (or preserving post-dive vitality, depending on how you look at it).
Studies conducted thus far on nitrox have not, I believe, looked into the issue of fatigue as a signifier of decompression stress and elevated micro-bubble score.... and whether nitrox use reduces these elements to preserve post-dive vitality.
Note: I say "preserve post-dive vitality".... the vitality you should have after the dive, given the relative physical stresses which your body is subjected to on a given dive, in comparison to your pre-dive vitality. Nitrox does not make you feel 'better' after a dive... it merely decreases the level of fatigue which a diver might otherwise have become accustomed to on their previous (non-nitrox) dives. That fatigue can be more significant if the diver maintains poor dive profiles and ascent behavior. It will be less significant in divers who otherwise maintain clean dive profiles and efficient ascent strategies.
In a nutshell: If you dive in a manner that elevates decompression stress, you might suffer post-dive fatigue (non-symptomatic DCI) due to higher microbubble score on surfacing. Nitrox use will reduce that decompression stress and the associated post-dive fatigue, compensating for some of the bad profile/ascent habits that exist. If you are accustomed to the post-dive symptoms of elevated decompression stress, nitrox use might reduce the fatigue you typically associate with diving, thus creating the 'illusion' that it makes you feel 'better' afterwards.
