This doesn't make sense to me. I have nothing to compare this experience of consciousness to. I know, logically speaking, that I am often unconscious (e.g. when sleeping), but there is no way -- by definition -- I can experience what that unconsciousness feels like. Thus, I cannot compare my experience of being conscious with the experience of being unconscious.

I don't see why this is a problem. Why should I need to compare my experience of being conscious to an experience, defined to be impossible, of being unconscious? If I want to compare it with something (although I don't see why I should need to, to have the experience) I can compare my experiences of myself at different times. It varies, even without drugs.

In what ways does it vary? Communicating internal experiences is difficult, especially when they may be idiosyncratic. When I first wake, my sense of presence is at a rather low level, but there is enough of it to be able to watch the rest of the process of properly waking up, which is like watching a slowly developing picture. There may be more dimensions to it than just intensity, but I haven't studied it much. Perhaps that would be something to explore in meditation, instead of just contemplating my own existence.