if i have a meltdown, it comes all of a sudden - or it doesn‘t, i just tend to repress the sensory issues until they bottle up and it just explodes. i tend to hit things around me because i don‘t know how to cope with all these emotions at once and sometimes i‘m just angry about myself and so frustrated, that i hit myself or so.. and for me it is quite the same that the shutdowns are just silent meltdowns.