Can someone please explain this to me?

Apparently I do it. But to me I feel no different to normal. So does this mean I've always done it?

I've googled, but really I must be thick because I still don't get it.

What is disassociation? How do you know you do it?

How can you tell when someone else is dissociating? What are the signs? What do you observe in someone dissassocating?