Half of face bright red after working out; Possible Harlequin syndrome?

Patient: Lately when I go to the gym and do lots of cardio half of my face is hot and bright red. It’s like there is a line straight down the middle of my face; the left side is hot and tomato red and the other side is either normal or sometimes a little flushed but just on my cheeks. It goes away after about 30 min-1 hour. It’s just on my face, not anywhere else on the left side of my body and there are no other symptoms (no change in HR, blurred vision, numbness, etc.)

Symptoms: Left half of face bright red when exercising

Doctor: