How to get rid of a stomachache from being disgusted?!

Hate to state the obvious but let yourself be sick & let it all out.
I agree it is one of the worst/bad taste films released lately ( ditto, ugh! ) I had the same reaction to The Cove.
It made me feel physically sick to the pit of my stomach, in the end I was sick & felt a little better.
No point in fighting the inevitable best to get it out of the way & recover.
Brought a can of ginger beer, let it go flat & warm to room temperature, took small sips & it settled my disturbed belly.
We never learn do we, we have to look!

EDIT.
Glad you're feeling a little better.

If you love animals, don't watch The Cove, after being sick, I cried & cried.

Have a shower. Put on something nice. Clean your teeth and have a glass of iced water. Take your time over all this. You are cherishing yourself. When that is done and you are feeling and looking good phone a friend to come and watch a NICE dvd or to go to a feel good movie. If it is a nice day go for a walk in a pretty park or garden. When you have done all that go home and do a chore you have been putting off.

I've seen that movie too... I can see why it would make you feel sick. It's not exactly what I would call gory or graphic but, the entire concept is beyond sick. I'm thankful to have a strong stomach.
You need to do something to help yourself forget about the movie. Put something else on, perhaps a comedy or romance... take a walk, call a friend. Just do something to get your mind off it.

Just relax and don't think about it. Occupy yourself with another activity or movie.

a couple of fingers over your tongue and down your throat and empty it all out.

what is the human centipede, and what channel does it come on?