I've only had a proper meltdown once (from extreme over-stimulation when I was forced to attend a really loud and crowded inter-school sport event). At some point I realised that I was scratching my hands, but my nails are quite short so it did no damage.
In the past (I was ~12) I scratched a place on my arm so much that the skin gradually wore away and it started bleeding. This process took about an hour, during which I knew what I was doing, but kept doing it. It wasn't really a meltdown, but I was very anxious and unhappy at that point in my life (because of my parents' treatment of me). Even though it wasn't deep, I still have a scar.
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Diagnosed: Autism Spectrum Disorder Level 1 without accompanying language impairment
I find it easiest to connect with people through the medium of fandoms, and enjoy the feeling of solidarity.
Too often, people say things they don't mean, and mean things they don't say.