hi there, so i started playing the game like 2 days ago, and for some reason my stamina bar has shrinked from 100 to 75

any idea on what could've produced that ? at this point i'm clueless

Likely some form of ailment, check your magic section, under active effects, any harmfull effects are coloured red.

The best way to get rid of any such debuffs is to visit, and pay your respects to a temple in any major city.

Disease.

yeah i should've guessed... thanks