I don’t know why this happens. There is no pattern that I can see, no set frequency or series of events priming me for it. And once it passes, it passes completely and I’m back to normal again. This chronic condition first surfaced in my teens, and persists to this very day. There is no known cure as even presenting something that normally makes me upset while I’m affected will not make me stop giggling.
When I was perhaps 15 or so, I called a friend long-distance (back when this was a Big Deal and you had to buy calling cards). I said hello and promptly was overcome with laughter. My friend was confused but then started laughing because I was laughing. We just held onto the phone and laughed for however long the calling card was for – 30 minutes or an hour most likely. The phone hung up and the giggleitis settled about ten minutes later.
If I ever start laughing and I can’t stop, don’t try to rationalize it. Just grin and laugh with me.