Seeing the title of your thread, reminded me that when I was around 17, I used to have this overwhelming feeling that I needed to go to the top of a remote mountain and scream and scream and scream to get everything out. I used to think it was a result of my rather crap childhood, but I realise now it was probably the existential stress as an (at the time) undiagnosed Aspie. I think others may have formed an opinion of me that I tend to get angry, my husband thinks I have a form of tantrum, but there are times when I have not been able to stop the anger/overwhelmedness from coming out, which is of course a meltdown. The rest of the time, I will fester like you, feeling the urge to explode but holding it in. There have been occasions when I have exploded in public, much to the disapproving looks of others. I think holding it in, is what results in having imaginary and dream meltdowns, as discussed in a recent thread.
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*Truth fears no trial*
DX AS & both daughters on the autistic spectrum