K.K.
It may have been a migraine. My son has had them since he was very small. Sometimes with head-pain and nausea and sometimes just lights flashing. He also has allergies, which may be an underlying cause. Sleeping or lying down in a dark room helps. Tylenol or Ibuprofin, if they can keep it down. When really bad, we gave him drammamine. It helps the nausea.