Welcome to the Migraine and Headaches Forum! This forum is for questions and support regarding migraine and headache issues such as: abdominal
migraines, headaches caused by allergies, cluster headaches,
headaches, headaches in children, migraine headaches, sinus headaches, tension headaches, visual disturbances.
Difference in pupil sizes is just normal for as long as the difference does not vary too much "A small amount of anisocoria or difference in pupil size is normal. On some days, a person’s right pupil might be larger than the left and on other days, the pupils might be the same size or the left might be larger than the right. But if more than a small difference in pupil size is present and persists, you may have a neurologic problem."
Source:http://www.nanosweb.org/patient_info/brochures/anisocoria.asp
However in your case, you have also experienced other associated symptoms like nausea and a sudden onset headache. I suggest that you have a follow up consult with your neurologist so that a complete neurologic and physical examination be done. Anisocoria may not need any further evaluation when there are no other associated symptoms .A referral to a neuroophthalmologist may be necessary.Migraine is only given as a diagnosis here when all other conditions have been ruled out. An infection, a vascular problem or effects of medications have to be excluded here.