I had two of those the fall of 2012, before I got sick with my current round off anxiety stuff. One at a meeting with parents, teachers and staff all sitting around a table (CSE conference as we call it). Didn't know what it was, thought maybe a stroke, but was not particularly anxious so I just waited it out and told someone later. Looked it up and found out it is a type of migraine without pain (I don't get standard migraines). Happened once again at the end of a school day. I think both times I was tired and possibly dehydrated. Never had them before, and hasn't happened since, don't know why they happened and what significance, if any, they have.