No, I wouldn't say meltdowns are abnormal in autistic adults. Even though we try to control them, we get into situations sometimes where we are completely overloaded and revert to atavistic behaviour.
I had a bad meltdown in the doctor's surgery 4 weeks ago because I thought she was
completely dismissing my concerns and making me out to be the one in the wrong because I was having sensory issues with noise where I work.
It ended up where I did quite a bit of damage to myself and she was just sitting there drumming her fingers on the desk! I need to see a doctor regularly to get repeats on my prescriptions.
Anyway, the following day I was told I had to see another doctor. It didn't go well either, especially when she said it was just too bad if I wasn't coping with the sensory issues and I started screaming (something I rarely do). Then when she later on suggested that I go back to my other doctor, I started swearing and screaming (again, things I usually don't do).
It is horrible feeling like a cornered rat and that is why adults still have meltdowns. I try and control myself for months at a time and then one day it gets too hard to stop the emotions from exploding outwards like an erupting volcano.
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Break out you Western girls,
Someday soon you're gonna rule the world.
Break out you Western girls,
Hold your heads up high.
"Western Girls" - Dragon