I have proof that neither of us are deranged! I've just read a most interesting non-fiction book called Dreaming Reality: how dreaming keeps us sane, or can drive us mad by Joe Griffin and Ivan Tyrrell. It's a whole new theory about why we dream and how dreams link in with depression.
Griffin and Tyrrell suggest that dreams are simply a metaphorical visual translation of things that are concerning us. Or more precisely, those unresolved things that are troubling us. Their theory of dreaming is that it's a way of discharging all the unresolved emotions that accumulate in the brain during the day. We don't just dream the thoughts directly, though, they're translated into visual metaphors -- hence the weirdness of many dreams.
They go on to suggest that this ability to use visual metaphors is intrinsic to the human mind and is strongly linked to creativity. Daydreaming (and the more focused versions that writers use to create fiction) is the human brain tapping what Griffin and Tyrrell call the REM state reality generator whilst still awake. Is it then surprising that, just as in dreams we interact with other human beings behaving in an apparently autonomous way, fictional characters can walk into their writer's head and appear to express desires and even argue with their creator? In fact, in the light of this new theory, it's a perfectly valid way of working and not at all peculiar. Refer anyone who says so to the book!