A lot of things changed when Steve got the serum. Some changes were obvious — like his size, strength, and agility. Some were more less obvious, like his mental processing speed or the inability to get sick. Since his was the first truly successful application of Erskine’s formula, he didn’t have a benchmark to compare his results to. There was a lot he didn’t know and no one to look to as an example.
So he didn’t notice at first that he couldn’t get dizzy anymore. In fact, it took Bucky reminding him of the Cyclone and the zipline ride that followed to make him realize that something was missing. There was no swoop in his stomach, no vertigo. No giddy laughter bubbling up through his chest to make his head feel lighter than air. He didn’t have time to experiment with it, though — that zipline was the beginning of the end.
After he woke up in the 21st century, he tested the theory, going to as many theme parks and roller coasters as his schedule allowed. The other Avengers gave him a hard time for it, calling him an adrenaline junkie — a fact he could not in good faith dispute — but it wasn’t all fun and games. He was trying to chase that old feeling, to see if he could find it. He never could.
But the first time Sam kissed him— well. That was a different story.