Really cool simple ruleset. I think it captures a sense of hopelessness as your vitality withers away that even more complex systems miss. it could even be applied to other stats like strength, sanity, social standing, etc xD
Starting at 20 could make gameplay stale with so many constant success in the beginning, but players could easily convert it to d6 or d12 to fit their game needs or just start with a lower value.
(i think you have a double space after "<" btw)