I was at a party, wasn't a huge event or anything, just my Gran's Christmas party, and maybe ten people were there, four of whom were my direct family, and the others were indirect family. After an hour or two and maybe two glasses of wine I had to go lie down in the quietest room available, and soon my family decided we should leave because they thought I was incredibly drunk or something. In the car they asked me if I was okay and I spontaneously burst into tears because I was so socially overwhelmed. I was 19 at that time. They stopped the car so I could go out and sob uncontrollably in the fresh air for a few minutes, after which we had to leave hurriedly because four men came to mug us in the dark street. People are so nice!
Anything even on the level of one phone ringing and one person talking to me simultaneously can trigger a kind of hugely paranoid shutdown where I just give up and everything around me is suddenly percieved as a personal threat, and I end up cowering with my face in my hands, if only for maybe five seconds or so. I drop everything and go straight to DEFCON 4.
If often like to think of it as being similar to a computer crash, like when you try to activate ten pieces of software at the same time and everything begins to judder and stops responding properly, and you sit and smash furiously at the buttons in a deranged fit (like me) but in the end you simply lose control until enough time has passed for the information to sort itself out.