My understanding of meltdowns is that they are the expression of a stress overload.
AS people experience stress differently to NTs. NTs experience stress in incremental increases, which can be managed and reduced fairly easily, preventing them from reaching overload.
AS people however, seem to experience stress in exponential increases, so that if not managed and reduced continually, they can very quickly and suddenly reach overload.
For AS people, during a stress overload meltdown, emotions may be totally overwhelming. This may impair cognitive functioning - the ability to hear, think, control one's behaviour, be reasoned with, etc. For some, this may even affect the ability to recall all aspects of the incident afterwards.
So....the trick is to be aware of all the things that cause stress, all of the things that reduce stress, and constantly monitor stress levels so that they are prevented from reaching the level where one more stressor will result in overload - and meltdown.
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"Our lives begin to end the day we become silent about things that matter." - Dr. Martin Luther King Jr.