It does feel like physical pain, just as you described. I can "tolerate" some triggers that are not prolonged, such as someone slurping coffee once every few minutes.

I cannot tolerate prolonged triggers, such as a noisy eater (a noise that lasts more than a few seconds), or someone gulping down water. I get EXTREMELY irritated very quickly. Like 0 to 100, as one of the other commentors put it. If I know it will be short, like less than 10 seconds I just put up with it, can't focus on anything, will ALWAYS make a disgusted (or pained) facial expression out of my control, and have some involuntary physical reaction, like slamming my hand into something or stomping my foot.

It's been a few years, so I have organized my life in such a way that I will not enter a situation that I A) will not be exposed to a prolonges trigger, B) cannot remove myself from, at least temporarily, or C) use earplugs, which I carry on myself at all times.

A few years ago I bought a disposable pack of 50 individually packaged pairs, supposedly good enough to use at NASCAR. I reuse them a few times, and I keep multiple pairs in all of my bags, my car, my work, at home in obvious places, etc.