Elaborate on your concerns. If you want it to be truly convincing you need to see the impact. That means a fake body, a costly endeavor involving an experienced special make-up effects artist. Or you could make a fake counter top and floor designed for stunts, use a trained stunt performer, and achieve a pretty decent shot. Catch is it needs to shot fast, as a slow motion shot will blow your illusion.

making low budget dreams come true

Or simple shots, good editing and effective sound will make a scene like that truly convincing.

=============================================
The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)

I agree with certified. Careful editing and sound effects.

For example have the actor put their head against the counter and then pull it up quickly. Reverse the film so that it looks like a head smack. Change the angle to capture them plopping to the ground in a lump. Add gruesome sound effects and perhaps a cut-away of blood on the counter and you can sell the effect.

In one of the making of documentaries on the Aliens disc Cameron said he used an effect like this for the face hugger. At one point they needed a fake facehugger to jump up on a toppled chair and then jump onto Ripley's face. His solution was two cuts. One was putting the facehugger on the chair and pulling it backwards and reversing the film so that it jumped up. The other was yanking the thing off of the chair towards Ripley, this time in fast motion. Quick cut-away to Ripley to hide the cut and I certainly never noticed the trickery.

RJSchwarz

Thanks for the ideas!