You are not losing your mind, lol. I have GAD, too. And I may have reacted the same as you did in that situation with the car. Panic can be triggered by literally anything when you have GAD. A few things I know will trigger me everytime: spiders, high winds during s thunderstorm (I live in tornado alley), a friend or relative going to the hospital, being yelled at or made to feel bad, crowds, being somewhere strange without someone I know with me, and being in a sports stadium! I avoid these things at all costs, as I HATE it when that rush of fear pours over my head. I have actually tailored my entire life to be as stress-free as possible. I know how to calm myself down, mostly. I live in the country, alone, with four cats. Family and my few friends are close enough to call and invite over or ask to visit. I keep my house silent for the most part, as loud noises startle me, and I have to sleep with white noise (a fan) for air circulation AND the noise: this eliminates any small-but-nerve-wracking noises my cats might make. AND I hear things that are not there sometimes, too - that drives me nuts. I'll hear a thud, or a squeak, or some other such noise (never voices, thank God), and wait to see if I hear it again before going to see what it is. So, no, you are totally 'normal' for having GAD. And kudos for knowing how to calm your breathing! Found a great link here:
http://www.helpguide.org/articles/anxiety/generalized-anxiety-disorder-gad.htm
Anxiety triggered by sound, music or smells is a classical Pavlovian conditioning scenario. Do a google search on Pavlovian conditioning and B.F. Skinner. There are easy techniques to disconnect the anxiety from the stimuli. Or see a behavioral therapist who knows about conditioning.