Whilst doing the reality check you are suppose to the same in your head. So while you are pinching your nose (or whatever your RC is) you should be asking youself some important questions. Such as

How did I get here?

What am I doing?

Is this a dream?

Hopefully once you have asked yourself them sort of questions you should be fully aware if you're dreaming or not.

I am not aware of anyone mistaking waking life for a dream. Not at least during the day. Perhaps it's possible to be confused when you have just woken though.