When I was 11, I suddenly realised everyone was going to die eventually, then cried uncontrollably, several times every day for a month because of the anxiety. It's only happened sporadically since then, like today, and it's absolutely fucking horrible. My coworkers are probably wondering why I spent 20 mins parked outside after work, too, and if anyone asks, I'll just have to reply, "Nothing," because I don't want to bum them out.
That happens to me when I will watch a certain movie that has a lot of death or when I can't sleep except it will be an anxiety/panic attack. It is horrible.