Trapped

[Kerbonzo_beenz]

So close to falling in.
Little half-slices peering over the threshold.
Darkness sucking my flashlights faint glow down like a straw.
From the air erupts hellacious screaming; it cascades off the cave walls.

From the bottom is my facsimile who stares back up at me, pondering oppositely.
I scream down at him and afterwards he screams back up at me.

The quiet is deafening here.
My head is spinning from it.
Suddenly I am falling weightlessly backwards.

From the bottom, I stare up at my opposite. 
I scream at him but he remains silent.

[dukealien]

So close to falling in.  Good grabber first line.
Little half-slices peering over the threshold.
Darkness sucking my flashlights faint glow down like a straw.  Apostrophe wouldn't hurt (flashlight's) although a second flashlight might be your reflection
From the air erupts hellacious screaming; it cascades off the cave walls.

From the bottom is my facsimile who stares back up at me, pondering oppositely.  Although "who" here helps personify the Other for later, it might flow better without both "is" and "who" (see below)
I scream down at him and afterwards he screams back up at me.

The quiet is deafening here.
My head is spinning from it.
Suddenly I am falling weightlessly backwards.

From the bottom, I stare up at my opposite.  Comma may not be necessary.
I scream at him but he remains silent.

Very visual - that's good.  The fifth line ("From the bottom is my facsimile who...") is a little problematic as to length and meaning.

In general, you use present participles (-ing) a lot.  This is good for immediacy and placing the whole narrative in the present.  You might consider changing up a few of these as you did in line 5 ("who stares" which could have been "who is staring") for variety.  It also eliminates the need for some form of "is" ("I fall" rather than "I am falling") but there are real advantages because  the way you've done it makes each line very immediate but also a little depersonalized, at a slight remove.

My only other critique is the usual advice to examine all instances of "the" for possible removal.  Save "the" for unique instances:  THE pope but A bishop.

It's a nice concept:  multiple personalities aware of each other but unable to communicate?

[TranquillityBase]

So close to falling in.
Little half-slices peering over the threshold.
Darkness sucking my flashlights faint glow down like a straw.
From the air erupts hellacious screaming; it cascades off the cave walls.

From the bottom is my facsimile who stares back up at me, pondering oppositely.
I scream down at him and afterwards he screams back up at me.

The quiet is deafening here.
My head is spinning from it.
Suddenly I am falling weightlessly backwards.

From the bottom, I stare up at my opposite. 
I scream at him but he remains silent.

Second line mystifies me, but I'm with you through the rest of the poem.  Just a couple of suggested cuts.  Enjoyed the read.

TqB

[Mark A Becker]

Hey k.beenz-
Some in-line suggestions, below:

So close to falling in.
Little half-slices peering over
the threshold.  can't see this image
Darkness sucks down
my flashlight's faint glow
like a straw. The air erupts
with hellacious screaming
cascading off the cave walls.

From the bottom my facsimile stares back
up at me, pondering.  image to describe please. "pondering" is telling, not showing. what did the pondering look like?
I scream down at him
and he screams back up at me.

The quiet is deafening here. very very cliche
My head is spinning from it.  from what? 
Suddenly I am falling weightlessly backwards.

Now I'm at the bottom,
staring up at my other.
I scream at him but he remains silent.  this ending fall flat. I get what yer saying, but it needs something more descriptive

It's an interesting conceit- the struggle with oneself.  But beenz, you need to visualize the scene and add descriptive language to draw your readers' interest.  I constantly struggle with descriptive language, especially imagery, but I can't expect a reader to see what is clear in my mind unless I find words to describe it.

Seems that you just threw this together then put it out here, but since this is BASIC, that's perfectly OK.
This could be a really cool piece with added detail.
Mark

[Kerbonzo_beenz]

Hey k.beenz-
Some in-line suggestions, below:

So close to falling in.
Little half-slices peering over
the threshold.  can't see this image
Darkness sucks down
my flashlight's faint glow
like a straw. The air erupts
with hellacious screaming
cascading off the cave walls.

From the bottom my facsimile stares back
up at me, pondering.  image to describe please. "pondering" is telling, not showing. what did the pondering look like?
I scream down at him
and he screams back up at me.

The quiet is deafening here. very very cliche
My head is spinning from it.  from what? 
Suddenly I am falling weightlessly backwards.

Now I'm at the bottom,
staring up at my other.
I scream at him but he remains silent.  this ending fall flat. I get what yer saying, but it needs something more descriptive

It's an interesting conceit- the struggle with oneself.  But beenz, you need to visualize the scene and add descriptive language to draw your readers' interest.  I constantly struggle with descriptive language, especially imagery, but I can't expect a reader to see what is clear in my mind unless I find words to describe it.

Seems that you just threw this together then put it out here, but since this is BASIC, that's perfectly OK.
This could be a really cool piece with added detail.
Mark

I am just learning now about how bad cliches are and how they dull a persons writing. I will look out for that in the future.
Always looking for helpful feedback so if any comes to mind I would really appreciate it.
In any case, however you interperet the poem is probably right.
I had something in mind that I thought at the time was pretty profound but later, when I verbalized it, it didn't make much sense.
Somebody mentioned that it could be about multiple personality disorder and it seemed to fit the bill pretty well so I went with that.
I feel that it strengthens one's writing when they have an actual concept of what they are trying to write about though.
So yeah, it was just something I mustered together, but I am proud of it nonetheless.