Hey Angie,
You're so creative, thinking of the chux to strain the nut milk - let nothing stand between a gal and her nut milk, I say!

Maybe it was the chux. Maybe it wasn't. Who knows? Chux might be impregnated with some nasties that have upset your stomach?
Until your nutmilk bag arrives, perhaps buy a cheap pair of panty hose or trouser socks - that might be a safer option. Or, if you have one of those bags for delicate lingerie - that could work too.
Another thing to consider..was the banana ripe? I know that any unripe fruit makes me feel really unwell almost instantly, and bananas are no exception.
I also find that I can only really drink nut milk based smoothies on an empty stomach, otherwise it can cause me grief. Did you have anything in your stomach when you had the nutmilk? Sometimes this can cause upset.
Perhaps if you try again in a day or so, on an empty tummy (with out the chux

) and see how it goes.
I have no idea on the fat content of almond milk, but almonds are not a "fatty" nut. Even though you're not actually eating the nut, you are eating the nut

because the nutmilk is made of water + whatever amount of nuts are mushed and don't end up in the pulp. But, I wouldn't worry about the fat content if you are eating lots of balancing fruit, veg & greens.