With me, my disassociation is a complete disconnect. It can last anywhere from a few minutes to a few hours, but I have no memory of what happened during that time.
It happens often when I'm driving (so I'll end up getting lost...a lot! and I'm almost always late getting places, because I'll "check out" and when I come to, I'm on the wrong side of town...or worse, back home again) even if I'm going somewhere I've been a million times before, I always try to have my GPS on to tell me where to go, otherwise I joke, I'll start off just needing to check the mail end up on the other side of the Gulf of Mexico.
It happens more when I'm under stress or upset about something, but sometimes it can happen for no reason, I simply shut down out of the blue. My therapist said there is always a reason, just that I am not aware of it and need to focus on finding out what triggers it.
But anyway, I *think* the biggest thing with it is disassociation is a disconnect from who you are and what you are doing. I've heard quite a bit of the alternate personalities like
@Go Hungry mentioned... I guess I don't have any alternates to fall back on, so I just completely check out and am mentally gone. Where to is anyone's guess.