Ah i missed that, i don't feel it should be something hidden if it improves the game, rather have it by default, you can make it limited (stamina bar or limited uses) or you could add it mid game in some later room. I'll give it another try, i really wanna see the ending!
Yeah, that's a good idea. I could add multiple Painkillers scattered around and each one allows you to run for a few minutes. The main character could start with an active Painkiller effect, so that when it runs out, he says something like "Ah! My back hurts! I need some Painkillers". The player would then immediately associate the slow walking animation to the Painkiller effect and look for one.
This could make up for some interesting situations!