Zoning out/shutting down

I’ve had problems for years with just zoning out or completely shutting down.  I don’t know what causes it sometimes, it’s like if I sit still everything shuts down and I either completely go to sleep or it’s like I’m asleep with my eyes being shut but I can hear things, but I just can’t respond or even move.  Does anyone else get this?  I was told it’s a response to being constantly overwhelmed and my body needing to rest from it all.  

Other times, like the three days annual leave I’ve had this week, i zone out for hours in a similar way, it’s very unproductive but it’s like I can’t fight it.  I had plans this week for my three days off but spent most of each day just lying still as if asleep but without being asleep.  Just zoned out and completely still.  I go back to work today and despite all this I feel completely exhausted.

does anyone else get this?  I read that it’s common for people with autism to be tired all the time.