Hey there Barbu, I just checked out the game. First, the idea of choosing when to heal and when to use the blood (red bar) as a resource is pretty neat. It makes it so the player has to use the resource strategically and I enjoyed that.
In terms of the difficulty, I got to the level where the white ghosts spawn but I couldn't get past it. I feel that a little time of invincibility after the player gets hit will make the game less difficult (which to me, it feels like a difficult game was something you were going for) but it will help it feel less unfair, so finding a balance between how much the player heals, and how much the player gets damaged when hit would help you keep the intended level of difficulty while giving players more time re-group before taking more damage.
The way the first monster you introduce gets knocked back when attacked feels great and really juicy, I wish more enemies had the same level of feedback when damaged -even though I understand this was a game jam game, and you probably had your plate full being a one-man team.
Keep going at it, and I be proud of what you accomplished so far :)