Most fantasy worlds work according to real physics with magic haphazardly tacked on. I want to build a world where physics works according to magic or, perhaps more accurately, how people in ancient cultures believed physics worked.
This magical world resembles a very, very poorly researched pastiche of various historical periods and cultures on Earth. The world is an artificial construct created by deities and is maintained by a vast bureaucracy of spirits and arbitrary whims rather than inviolate laws of physics. Gravity is the result of the flying spaghetti monster holding everything down with his noodly appendages, disease is the result of disease spirits rather than pathogens, weather and natural disasters are the work of spirits, etc. Obsolete scientific theories like spontaneous generation, miasma theory of disease, orgone energy, four humors and so forth are also true. There's no distinction between magic and mundane science, and sufficiently talented or skilled individuals are capable of ignoring these rules (e.g. so skilled at healing you may raise the dead, so skilled at swordplay you can cut mountains in half, etc).
However, this runs into problems if you examine things too closely. For example, how does nutrition and nutrient deficiency work? If people are dying of rickets and scurvy despite cellular biology not existing and no way for the primitive cultures to understand why, what is the cause and why are these afflictions cured same way they are in the real world (i.e. sunlight exposure, eating onions)? Are scurvy spirits repelled by onions?
Or should I just take the Game of Thrones approach and give everyone better dental, height and overall health than in the real world because it isn't the real world, biology doesn't actually exist, and most of my readers wouldn't actually care about the extreme departures from reality? It does seem awfully inconvenient for major characters to die of simple infections because that would be realistic even though it would drag the narrative to a screeching halt.