Consciousness can't change either, because a change in consciousness changes everything that is experienced, so how can you know whether everything or consciousness changed? There's no difference.

Some terms can only be defined in terms of themselves. What's a meter? It's term used to describe a length of measurement equivalent to one meter. What's consciousness? It's a term used by certain life forms to describe what life is.

How can we study something that's always there, and when it isn't there we're not there either? Everyone "experiences" the absence of consciousness in deep sleep, and there's simply nothing there.