Shutdowns, Meltdowns or something else?

Hi All,

I've been trying to understand my experiences in the context of things like Meltdowns, Overload and Shutdowns.  I've been struggling to match my experiences to the terms though and was hoping people here could help give insights into them to match them up.  Or are they just typical human emotions that aren't autism related?

For example:

• After being in London for too long, I can commonly go into a fetal position on the train, be unresponsive and have my fingers in my ears with my eyes closed.
• I can get into states where even through noise cancelling headphones with music playing, it feels like everyone is shouting around me
• I can get catatonic in stressful situations or after a hard week - is that a shut down?  Or is a shut down like at the end of the day where I just can't function other than to lay in bed and listen to a familiar TV Series?  Or are they on a scale?

I've had an episode where I saw someone linked to a past traumatic event and after a few minutes went completely non-verbal, heavy breathing, collapsed to the ground next to my car kind of thing.  Is this an implosive version of a meltdown?  Is it an anxiety attack, or does that tend to have more thoughts and fears along with it?

I find identifying meltdowns particularly tricky given that I'm not prone to violence or aggression particularly, which in most online research tends to get linked to meltdowns.

So how do you know the difference between a shutdown, a meltdown, or something else?

Any insights or questions welcome!

Thanks,
Craig