Part if it is just getting used to that stimulous (tones). Often times they are loud and abrupt. That and just getting experience of working critical calls and learning to focus your attention on scene.
Honestly, it isn't a feeling of suspense anymore. I hang out with my partner, read, and just do things I want to do while I'm not on a call. Tones don't get the same reaction simply because I've heard them thousands of times. It's all just a matter of repition. It also doesn't help I don't have those God awful fire station tones that give you tinitis, I'd probably **** my pants if I went back to those.
As far as nervous on the way, not really. If I knew I was going to a bad peds call, probably. But the 99% of what our day to day is are all relatively straight forward situations. Much of what I do is simply respiratory, minor falls, drunks, overdoses, psychiatric issues, etc. Just a little common sense and being a decent person to your patient will get you through those.
That being said, that call is an excellent example of why you let the notes be a guide, not an absolute. You will walk into situations like that and be completely caught off guard by what you find (hopefully still prepared) and others will sound serious and they turn out to be a whole lot of nothing. Chest pain is one to always expect the possibility of a rapid change. I've been in that same situation as have most here probably.
Give it time. You will get to where being dispatched to an arrest doesn't even get you nervous. Learn from past calls and partners, get familiar with how to do the job, always learn more, and you will settle into a groove.