What is it about fizzy drinks that make them irresistible?

No. It just tickles your nose. A not unpleasant feeling. 

I love carbonated drinks. Just spent money on a Kitchen Aid carbonated beverage maker. I get the most pleasure from carbonated drinks when they cause tingling in my throat. It reminds me of the cola drinks when I was a kid, and the sodas tickled/burned my throat when I drank them. I like it plain, with artificially sweetened flavorings and most of all with Scot's whisky.

It isn't so much the CO2, but the sugar and caffeine that triggers your brain and makes it want more, and also the sodium that leaves you thirsty, making you think you want more soda.