The game is a great one, no doubt about that. And the fact that, the game was made within 20 hours, awesome work man. the name is the very first thing that caught my undevided attention. the game gave me very good scare, I will be looking into your other games asa i make some time.
I have some suggesstions for your consideration, just in case you ever release further versions.
* The part where you cannot go up was a really good concept, but describing this information straight forward kind of ruined a great chance of surprise element for the player. why not let the player go 2/3 floors down and then put him in a situation where he have to go back to search for something and while trying he discovers that, he cannot go up. Then some note appears, where the messge is loosely written...
* There is a great oppurtunity for a complete story with an awe ending. for example, before playing i had an ending in my mind. I was thinking, at the end i might find myself dead in the car. at the very begining of the game i tried to look inside the car, but from the driving side the inside view was blocked. which made me think this ending. also the name, THY FLESH which can be translated to your flesh.
* the maze was kind of repetitive compared to a linear gameplay, but great sound effects. amazing work.