I added HP and MP regen to "screen inventory_screen()" in inventory.rpy, generally quite useful, imo
text "MP regen: [h.regen[mp]]" style "inventory_stats" text "HP regen: [h.regen[hp]]" style "inventory_stats"
and you're right, the base value for HP is -1. my MC is suicidal, too much talking with Klaus, I presume :D