Audience to perform
Resolves if goal is accomplished
Age: 1-5 years
Continues without attention
Safety may be compromised
Not goal dependent
May require assistance to regain control.
Age: through adulthood
See, when I get overwhelmed, curl up in a corner, cry, shake, and pretty much don't acknowledge your existence/want you to leave me alone, and if you do leave me alone, I keep crying and shaking just as much as when you stay with me, that's not a tantrum. That's a meltdown.
When I'm overtired, coming down off sensory overload, have been triggered by song lyrics, and then find out that I wont be getting food until after the time when I would normally want to be asleep, so I curl up the corner of the hotel room and start to cry, choosing the corner I did as the one where I figured my roommate would be the LEAST likely to notice, that's not a tantrum. That's not culture shock either- none of those had anything to do with the culture of India. That's a meltdown.
Having gone to the professor after getting myself back under control and asking for help doesn't retroactively turn the meltdown into a tantrum. If it were a tantrum, I'd have had it in front of whoever I wanted help from and continued until I got it. Instead, I knew it was coming, got myself OUT, had it as privately as I could, and then went to deal with the causes once I was rational again. I have no illusions that I'm rational during a meltdown.
As far as dangerous goes, some of us have dangerous meltdowns, and some of us don't. The worst you're going to get out of me is a rant about whatever caused the meltdown spluttered out between the tears and the gasps. (Normal crying has long since stopped giving me breathing problems, but meltdowns still make my breathing a little weird. Not dangerous weird, but I am out of breath.) I could also be rocking/shaking, which also aren't dangerous.
And fixing the problem won't end the meltdown. It takes away the cause, but I'm still melted down, and I still need to get myself back under control. It's not an immediate off switch. (Note that I'm often well away from the trigger by the time I actually melt down. I'm pretty good at delaying meltdowns, but if it's coming, it's coming.)