But the taste alone probably makes you vomit

Your brain can't tell the difference and tallies the perceived callories that wind up going unused until you exacuate the waste.

Depends which sweetener?

Possible that the sweetener makes your body believe it’s sugar enough to puke?

Not sure.

Some artificial sweeteners contain molecules that taste sweet, but are too big for the body to absorb. But they still have to go somewhere, so the body gets rid of them, violently, at either alpha or omega.

If you recall Amazon's huge bag of Satan's sugar-free gummy bears, that's the same stuff.