Like Christina, I have had a few (more than two) of these meltdowns in my life (and they are not characteristic of my usual self)----I felt embarrassed (I once left a job over this even when the boss tried to keep me I was just so ashamed)
because I never saw them coming.
Usually, it was a result of either being just really physically or emotionally tired or 'triggered' by something I didn't expect but should have...again usually tired...stressed...
It has made me much more tolerant of others having a meltdown, and more likely to try to do something to help that person (eg: at work one day when I was filling in as an agency staff, a man came roaring into the office screaming at the staff behind the counter about his bill, began to climb over the counter at them; and I was able to walk over, talk him away with me to 'resolve' the issue. It turned out he was wrong and the bill was correct but I took time to sit with him and review the records until he saw that himself.
(if someone is doing this is intoxicated or having psychotic experiences the approach is different...)