Well a dream is as real as things get.
The whole problem is really in describing reality. Ask any lucid dreamer and they will explain you than the key to lucid dreaming is to constantly question your current state(are your dreaming or not?).
And after some time it just doesn't matter. Because every thing is just a electrical impulse to your brain. If your brain is sent a signal to treat hot as cold. You will hold a hot iron in your hands and be perfectly OK with it. The reality of things 'hot being hot' doesn't change, nothing changes but your perception of things.
If you ponder deep enough when you dream this is what happens in a dream too. You are perceiving things. Whether they are real are not, is as useless argument because your knowledge of it is the way your brain is telling you about it and not what it actually is.
I've had inception like dream within dream, losing lucidity while dreaming inside the dream and there after. In stages like that its difficult to say what is reality and what isn't. The safest way is to not do any thing harmful or dangerous. In fact I didn't know of it until I woke, it was then during a usual dream recall that I got a surreal feeling that I had woke up from three levels of 'reality'.