It's like that, but it's existential, too, not just sensory like vertigo or something. It's a sort of anxiety attack, or a lot like
jamais vu.
The closest approximation of it is to imagine seeing yourself in the third person or the world shifting like in Jaws when Brody's sitting on the beach.
EDIT:
http://en.wikipedia.org/wiki/Derealization
I don't like that Linden website's definition.
