Nice!
The darkness bit was a bit disorientating at first. I thought the game had crashed or I had lost or something :P
But after I realised that it was part of the game I thought it was quite good.
One suggestion I would make is to have some UI that shows the player the game is still running even if you cant see anything. Like a head grow back timer or some text saying “Regrowth in progress” or something like that.