A trigger to me when i try to explain it to 'normal' people is like this:
I just watched my pet get hit by a car in the morning, right before work (horror), then I sat in a traffic jam with no apparent reason for the traffic (frustration), knowing that my boss had already told me I was going to be fired if I was ever late (expected outcome), the tension of sitting in traffic anticipating what is going to happen to my family if I lose my job (anticipation and catasrophizing), the fear of walking in the front door when I finally get into work (anticipation and anxiety), spilling coffee on my shirt because I am so anxious about losing my job (feeling stupid), Walking through the front door knowing that I will have to walk by the bosses office in order to get to my office (anticipation and anxiety). The boss screaming at me even though I am trying to explain (not being heard) and telling me that he will decide by the end of the day whether I will lose my job or not (the unknown) but to GET TO WORK (performance anxiety) you lazy so and so (shame), people at work sneering at me because I am upset and they don't know what has happened (not being heard, shame, judgement). Barely able to speak to clients on the phone (performance anxiety) because I am frozen with fear (panic) that in this one day my entire life may change in an incredibly horrific way (anticipation, fear of the unknown). And it is my birthday and nobody - not even my wife has noticed (dismissal).
All of this in one day is too much for most. But during a trigger it happens in an instant, overwhelming one for the rest of the day or longer with all of the feelings in brackets hitting one in a single moment overwhelming the system and causing a reaction that is real but that others do not understand because they either don't understand or can't be bothered to care.