It's been a couple of decades since I last had an actual meltdown, which usually consisted of either verbally lashing out at whoever was around or abruptly disappearing, always in response to being overloaded with too many people, too much socializing expected of me, too much random noise, etc. Since then I've gradually learned to detach and withdraw into my usual uncommunicative state, just observing quietly from as far away as possible. I keep getting better at this, though finally getting out into fresh air and a place where nobody will even notice me is always welcome.
"Mini-meltdowns" still happen a few times a week however, but only last a few seconds at the most, always when I am alone, and are basically no more than loudly repeating a word or phrase a few times before I calm down. Since this only occurs when I'm alone, it seems to be of a much different type than what I was going through years ago, which were always in or around large numbers of people and went on for some time, or until I could escape. I hope more meditation will eventually help.