Richard Feynman poses a very interesting question in his book that I just read. He asks another scientist to define what is "real." The other guy says that an experience is real if it can be reproduced. Feynman then goes on to talk about reproducing hallucinations. He says that if one thinks about a particular subject before going into a mental state that invokes hallucinations (There's a whole process to it. You have to read it for yourself to know more about it.) then the hallucination will be related to that subject. And you can do it multiple times. That makes the hallucination "real."
There was this movie called 15 Park Avenue that dealt with schizophrenia. The doctor in that movie told a patient's sister that the schizophrenics' world is as real to them as ours is to us. Their reality is what they perceive, ours is what we perceive. Doesn't each of us imagine things that don't actually exist? It's perfectly normal to imagine that someone you fancy could want you as well, while knowing fully well that the odds of that happening are rock bottom. What Konkona imagined in that movie was basically an exaggerated version of that. We're all a little bit like her, a little crazy.
I still don't have an answer to what I started out with - what is reality? Any ideas, anyone?