Some on-the-fly remarks:

1. Controls are QWERTY-only instead of layout-independent, but the arrow keys are enabled.
2. Several controls (left click, Left Control, Left Shift, Alt Gr, Space); I think you should indicate them either in the game or/and on the game page. For example, you did show the E key in game, which is a good thing. :)
3. If you stop crouching while inside the tunnel/duct, the character still stands up, which results in a buggy view from inside the wall.
4. In the first corridor after the fall, is it normal to fall through the floor if you cannot escape the moving walls?
5. By the way, you really have to rush for it immediately!! Maybe you should only trigger the walls when the player is closer? Or is there a key for running? Oh yes, there is: middle click! XD Which makes my advice about showing the controls even more crucial.
6. Ah, so this is your first game! Congratulations. :)
7. Small language point: I am not a native English speaker (I am French), but I am not sure you can say ‘motor’ instead of ‘engine’ for a game engine. I may be mistaken!
8. Not sure the cat matches the atmosphere. Let us put this down to the madness theme. ;)

The game was a bit short, but I think it served as a test for you, mainly for designing a level. There were some ideas, including the wall trap and the line you have to walk onto; you could surely extend this into a full-blown asylum full of such weird traps. :)

I guess the link to the constraint is that it is all happening inside the player’s head, and this is what your sentence in the form suggests.

Some music could help strengthen the ambience. :)

I see the game as a first dive into 3D first-person level design!