I was initially diagnosed with cluster headaches by my ENT when I made an appointment after I had insisted on a sinus infection due to the pain, congestion, swelling eye, and so on. Antibiotics were no relief and imaging of my head and sinuses was clear. I then saw a neurologist who confirmed this diagnosis, and am being treated by my primary care physician who is closer to home than my specialists. Imaging is a must, other clinical signs are observed or described by the sufferer during an attack, such as agitation, pacing, autonomic signs like slowed pupil response on the affected side, congestion, tearing, swelling, and of course improvement of symptoms with the administration of high-flow oxygen is a big indicator!