Horner's Syndrom(syndrome)

I have recently been diagnosed with horner's syndrome.  About 2 months ago I noticed a droppiness in my eyelid and a difference in my pupil size.  I have seen a neurologist who has given me and MRI of both my head and neck.  A MRA of both head and neck.  Also CT scan of my chest.  They have not found anything on any of the tests they have given me.  Last night I was at an exercise class and when I got home I noticed the right side of my face was very red and sweaty, also a little swollen.  The left side of my face had none of these effects,  Now they want to do another MRI with contrast.  Just wondering is this completley necessary?  I thought the lack of sweating on one side of your face was a side effect to horners.  Are all these tests really needed and isn't it sometimes they don't find a reason for this horner's syndrome.  I need some advice.  Stumped in wisconsin.