Another theory is that carbonated water increases the amount of CO2 in your system, which typically helps regulate mood. Same school of thought as doing breath retention work ala wim hof or buteyko
oh it's interesting to think of carbonation as fulfilling a similar function as breathwork. i do find that if i haven't had soda in too long i start to crave the carbonation specifically. hmm
for me it was the minerals-
as long as u buy the kind with rock shavings and dont just blow fizz into your tapwater, using one of those at home selzer devices