I had similar responses when I was younger to varying stimuli, not necessarily crowds though.
The thing I learned was to know your boundaries well, to know exactly what you can manage and can't manage and to actively avoid situations that you can't manage and to have a plan set in place if you are in a situation you can't manage. For example, trying to get to target before the crowds got there was good, so you did good in that regard because you thought before hand that there would be crowds there so you actively attempted to avoid the stimuli you already knew would be bad for you, so for that good job! But, things you haven't counted on do happen, so you may need to find a plan when you do find yourself in a situation that's not very good.
For crowded areas, I find the general idea is that there's so much going on, so much over stimulation that you can't really handle it, you can't feel safe in that situation because it's simply impossible to keep track of everything. A remedy for this that may help is to just focus on one thing when in a crowded situation, just one thing. For example, if you are in a line, just focus on the person in front of you. Look at his back, what shirt is he wearing? What material is it made of? What kind of pattern does it have? What is he doing? Is he on his phone? Is he talking? Listen in to his conversation, see what he's talking about (but don't talk to him or anything, just quietly listen). Only focus on HIM and him alone, no one else, just try to intently focus on him. Obviously don't just stare at his face cause that might make him uncomfortable, but just be a quiet observer, attempting to get as much information about this person as you can until he goes away and its your turn to do the line. Focusing on one thing will help drown out everything else and may stop the overstimulation.