I think I have shutdowns rather than meltdowns. I essentially go very uncommunicative.
The one meltdown I recall came after a brief holiday (four nights) with pre-marriage Mrs Hopper when I was 19. We travelled by coach. When we alighted at the station on our way back, I realised I didn't have my wallet. I ran back on the coach, but couldn't find it anywhere. I became more and more agitated, pacing about and talking angrily to myself like the cliche weirdo, Mrs Hopper trying to calm me and concerned about me causing a scene, and it came to me crouching against a wall in the station speaking low but with force and anger in response to her telling me to calm down, thumping myself in the head and rocking backwards and forwards with some force. I think it maybe lasted ten minutes or so, and I went from that into a shutdown for the rest of the afternoon.
I'll sometimes get close to a mini version of that if I'm on my own. Kind of... grumbling to myself (somewhere between growling and mumbling), pacing a lot and breathing heavily through my nose. But I generally keep it 'tight', and shutdown instead.
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Of course, it's probably quite a bit more complicated than that.
You know sometimes, between the dames and the horses, I don't even know why I put my hat on.