horner's syndrome and tumors of the brain and lung

I am scheduled to see a neurologist next week to due tests for Horners Syndrome.  I have a constricted pupil in my right eye (does not respond to light or dark stays small all the time)  my left pupil responds normally to light and dark.
I do not have drooping eyelids which is what you usually see with Horner Syndrome, however my doctor thinks I have Horner Syndrome and is sending me to a neurologist.  I have read that the underlying cause of horners is usually a vascular problem pertaining to a brain tumor or Pancoast tumor of the upper lung.  Something is definitely disrupting the conection between my brain and my eye.  The doctor found no inside pressure on the back of my eyes.  He does not think I have the alternative condition Aide's pupil because my symptoms are atypical.  I have sholder pain on my left sholder most of the time and some headaches and neck pain and mild ear pain on the right side of my head, the side that has the small pupil.  I am so afraid that I have brain cancer or lung cancer.  Do I have symptoms of a brain tumor or pancoast tumor of the lung?  Does this sound very serious to you?  Are my symptoms indicating that I might have another kind of brain tumor?  Thankyou in advance for your answer on this, I am really scarred.