Zombies In Dangerous Dungeon

Waking from the cold and opening my eyes, I realize that I am in a wet dungeon or cave. Only rustling wind and droplets of water can be heard.

My whole body is awfully sore and it's so dark I my eyes can barely make out anything. What happened?
I cannot remember anything. Maybe it's just a terrible joke? Suddenly I hear a strange and terrible sound, a sound unlike any other I've heard.
A sound that is not produced by any living being... I searched my pockets and found a flashlight. Hooray. It's getting lighter but blood is seeping in. Blood floods your eyes and it's hard to see what's going on.
I try to look around as best as I can, but see no exit. And the sounds are getting closer...
I obviously need to get the hell out of this terrible cave immediately! Suddenly a head is illuminated by the beam of my flashlight. Horror strikes. This is the head of a zombie. I must run as fast as I can to get away now!
Suddenly I stumble upon a sharp object and find that it's a gun. Well that's certainly helpful. Although I do not remember anything, it feels comfortable in my hand as I'm used to handling weapons.
With weapons, I'm already a hero. Picking up the gun with a flashlight, it becomes easier to see. After standing until my eyes adjust, I wait for the zombies.
The first zombie I kill with one shot in the head. But a second is right behind it. My eyes dazzle from the muzzle flash, and my head is pounding.
Having destroyed two zombies, I make my way through the dark dungeon further. I find more weapons. This time it's a machine gun. Now I can kill zombies more efficiently.
Somehow though, I must survive and find a way out.

Control keys:
0,1,2,3,4,5,6,7,8,9 - Change of weapon
WASD - Character movement
SPACEBAR - Jump
SHIFT - Sprint
Esc - Exit the menu
LMB - Shoot
RMB - Aim