Dear F & 2S,
I've never had much luck with pantoums, and don't know that I can be very helpful for you here. I assume that you've got the two refrain lines moving in the proper order. You have an issue with the metrics of your lines. It's unclear in several cases whether you are using a four foot line or a three foot line, and whether you intend to have some of your feet scan as three syllable or two syllable feet. I think at this stage of things, you will want to be more distinct with the identity of the feet you've chosen; they will have a substantial effect on the sound of your line.
(I use "your line" here as a way of talking about the sort of line you've chosen —consciously or not — to use as the staple line in a given sort of poem. The sort of line that the poem in general seems to fall into. The "factory settings" the poem seems to come with. You can put them there on purpose, or your unconscious will kick in and put them there for you. In this case, as a relative beginner, your unconscious has chosen something closer to a free verse line. If you want to write something formal as a pantoum, you will have to go back and regularize it to some extent, to fit with the rules of the game you've chosen to play — the Pantoum game, in this case.)
In a poem of this sort, you'd probably want more regularity in your meter to convey a unity of effect. It's a short poem, and in a poem this short which seems to want to set up metrical expectations, any variation from them will tend to underline itself. Therefore it should be varied from only at a point of significance in the poem, to underline the significance of the meaning at that point as well. You can break the rule as you wish, but each time you do, you should make a careful note of what the actual effect is on the poem you're writing, so you can make a decision for yourself if that rule is one that is useful for you in that instance. The rules are helpful and meant to be helpful; they aren't meant to confine you. Break all that you need to. The poem is the final judge.
Down darkness we free fall
Before a bullet reaches our backs
We try to break away from it all
But we're bombarded by attacks
So let's have a look at the first stanza. "[W]e free fall is straightforward. "Down darkness" to my mind is not. I like the sound of the two d's playing against each other, but while there is some lovely sonic play here, we're a little short of visual orientation or sense of place. Lack of punctuation is an interesting experiment, but probably doesn't work remarkably well in formal verse, where you can't use line-endings to make play with the ambiguities in the way to might in free verse.
"Through darkness, we free fall" is what I think you mean. You've been forced to tinker with the order of the clauses a bit to force the rhyme, though, since normal order would be "We free fall through darkness." There's nothing wrong with your order, by the way, I simply grumble about these things because I was a bear in a previous life, and I can't seem to get over growling.
The other thing to notice about line one is that it's a three foot line. I'd call it iambic trimeter because I'm placing the accent of the second syllable of the third foot, free FALL, though the difference in stress isn't huge. We generally look at the first line to see what the metrics of the poem are going to be, and it's generally a good guide. If the first line is five feet, the poem's usually in five foot lines, if it's three feet, the poems in three foot lines and so on. Here, the first lines is three feet, and the next line is four feet. There will be variations through the rest of the poem, three lines, four lines, though not in any order that I've been able to find. In further drafts, you'll want to decide if you want to fix that or find some way of playing with that. With a pantoum, I'd suggest regularizing it and cutting way down on the metrical variations, to give the poem a clear metrical underbeat.
Instead of "'a' bullet" I'd suggest "'the' bullet" because it makes a more particular statement. "A" bullet could be any bullet. "The" bullet means a bullet we should know something about and which is therefore for ominous.
"We try to break away from it all" takes an opportunity to place the reader in the middle of the situation that you suggest is so threatening and passes on it. "It all" could be the pillow fight in the lollypop factory (and we all know how sticky a situation that could be) to a two aspirin headache (Oh, Ouch!) to deciding that you won't take part in animal testing any more. In the poem, your job is to choose none of these things yet live up to the drama of the set up you've given us so far. Or say something specific and terrible in this line and revise backwards to fit the specific and terrifying thing that you venture here to supporting stuff that comes before. Additionally, the final foot of this line is an anapest. It really throws momentum and weight toward the end of the line. It's worth listening to how that foot affects the movement of the line and how it throws weight at the end, simply because it's a good example of how this sort of piece of metric works. Notice what you see it doing to the beginning of the next line as well. Try changing the end of that third line to something more iambic and see what it does to the beginning of the fourth line and see if you can get some feeling sense of what the difference is for you.
As always, you'll notice that the poem is suffering from the lack of specificity. Feeling everywhere assailed will be different experientially if it is by gnats or ninjas.
I'm running out of time here, sorry to say, but if you can possibly find a way to read an eight page poem by James Dickey, I think you will find it an amazing experience. The poem's called "Falling" and I think you might be able to come back to this poem with a new set of eyes about detailing and specificity and entering into a poem after having a look at that one. I'd very much like to hear what your reaction is.
Sincerely, Bob Kaven