“Real” in the sense it exists within your mind, which exists (somehow) within your brain, which is itself likely real. So your imagination must have some physical basis, but it would exist entirely within your brain (or body, to the extent the rest of your body influences the brain itself).
Your brain imagining a specter in a doorway does not mean there is any anomaly within the physical space of the doorway at all that anyone else could perceive or measure - they would need to measure your brain to (theoretically) detect the physical basis of it.
What you see, feel, hear, taste is an interpretation of your physical environment, and may not accurately reflect it at all times.
It’s interesting, because there are textbooks that say the magnetic field lines aren’t real, but are a good visual of what happens when a magnetic particle is there…
Yes field lines are just an indicator of where the field is - a bit like how maps have contours showing height above sea level; those contours aren't physical things but they describe the physical environment in a schematic way.
I know funny isn't really the goal for comments around here but man that made me laugh. So subtle and obvious at the same time and quite an appropriate response to the posed question!
To tack on to the amount of complexity; your brain’s operation allows you to perceive a world outside your brain, but the actual perceiving of it happens inside your brain, which again rests inside the perceived world more or less..
Your brain imagining a specter in a doorway does not mean there is any anomaly within the physical space of the doorway at all that anyone else could perceive or measure - they would need to measure your brain to (theoretically) detect the physical basis of it.
What you see, feel, hear, taste is an interpretation of your physical environment, and may not accurately reflect it at all times.