I do not know the day. Nor the month. Nor the year. I do know, however, that I am American. And I am a prisoner of war. And there is a large, festering wound below my knee cap. The flesh was torn off, but the blood is dry by now. All that remains is black, rotting skin, and the faint outline of my bone. Some days, it aches so badly I feel as if I am dwelling in hell itself. Other times, I can sleep for about three hours without experiencing any sharp pain, and I am able to cope with the steady throbbing.
I found this pad and pencil in my backpack, which they left me. My gun, of course, has disappeared, as have my shoes. The cell, I have determined, is more than five stories high, and I catch the cold wind from the elevation every time a storm sweeps through. I know I am no longer in my country, because I hear the voices. They mumble outside my chamber every time they  throw me food or a thin, flea-infested blanket. I used to scream profanities at them, questioning why they had done this to me, insulting their inhumanity. But it did nothing, except make me even more depressed, as my screams turned to wails and my wails into sobs.
The reason, however, why I am writing all of this down is not to complain. I have had plenty of time to wallow in self pity, and I am positive I will have much more.  As much as I want to believe that one day I will be reunited with my past life, it seems as distant as the stars, and I have lost hope long ago. My memories of happiness all faded into my subconscious, reigniting only in my dreams, and when I awake they are gone once more. So the optimism has ceased, but the thinking has not. I have flashbacks, periodically, of the war I was fighting in Vietnam, the people I was with, the things I saw. And this is how I arrived at my conclusion, this is how I know why I am trapped, this is what really happened:

The gunfire had ceased for about ten minutes. I was lying on thick forest ground, crawling through beds of weeds and grass, next to my fellow comrades. We were to seek out a village about a mile down, and be sure that all enemy soldiers resting there were killed before nightfall. But something had gone wrong, one of our men had prematurely fired, and our plan was exposed. Thus we had to regroup and take a different approach, knowing know that the rivals were prepared for our infamous arrival.
So we inched along, and after the ten minutes of silence, a grenade exploded to the left of me. I caught the repercussions of its painstaking sound, which made my ears ache and head pound. I screamed but my voice was drowned out by the mass destruction following the attack. The guy next to me- whose name has vanished in my mind- turned to face me, his ear steadily dripping viscous, watery blood. I did not and could not move for what felt like forever, until the unbearable sounds became a steady hum, and the throbbing in my ears became tolerable.
I remember army crawling for a long time before I heard the piercing scream of what sounded like a woman. Although it was much quieter than the grenade explosion, it seemed to echo inside of my head much longer, causing my body to quiver.  I rolled behind a nearby shrub and positioned my gun so that in aimed in the direction of the scream. I heard feet padding towards me, picking up rapid speed. I had no intentions of shooting an innocent civilian, but I positioned to fire and rested my finger loosely on the trigger.
The screamed turned into a cry, one of sharp pain, about thirty feet away from me. I sat up slightly and peered beyond the bush, and thus had a better view.  I could only see the top of the woman's body, sprawled out in an open patch of dirt, her hair caked in blood. The scene itself was horrifying before I saw the thing chasing her.
I will not address it as a beast, for it had no qualities of any earthlike body I've ever seen. It was a thing. 
It came shortly after, moving at a steady pace. It had thin legs, but at least 5 of them, which it used to carry its body and lanky arms. It was all black, with no fur, only a thin layer of slimy skin. The face was only identifiable because of the teeth, which weren't really teeth at all. They looked like daggers, at least 5 feet long. This thing was huge, the size of an average tool shed. It grazed around the body before sinking its "teeth" back into the woman who was now beyond dead.
Blood poured out of her, and covered the beast which did not flinch. I shuddered, looked down, and realized I had dropped my gun and released my bladder. I shook violently at the sight, but I was frozen. That is something I distinctly remember: I could not move at all.
I watched this helpless human get devoured piece by piece, and I could hear her bones cracking with each bite. The sight made me sick, which was reflected by the amount of vomit that accumulated on my uniform before the thing was finished. I have no recollection of how long I stayed there, but I do remember arms coming around my body and throwing my to the ground. It caught me off guard completely, and knocked the breath out of me. I was punched, hard, across the face, so hard I spit up a tooth.
"He saw it, he saw it."
Those are the only words I remember hearing before I was shot in the leg and proceeded to black out. The next time I woke up I saw only darkness, felt only pain, heard only my heart beat.
And so, thus, I am here. It has been a while, I know that, but I do not know how long. I desperately need someone to find this note, get word out to my country, and save me from this hell I am living in. I know, for a fact, that there is a thing out there, much more dangerous than any creature on Earth. It is not only Vietnam in danger, it is the entire world.
I do not know why I have been kept alive, but I hope I do not waste away in here. If that is my fate, I hope to die shortly. Please, whoever finds this, do not take it as some sort of joke. Take it as a warning. You are in danger.
You are all in danger.