Something Occurred Today That Has Never Happened Before. I Had

Something occurred today that has never happened before. I had a sudden wave of something that made me feel like I was going to fall asleep... Or black out. I felt like my eyes had to close and things momentarily got dark and then it passed. I was in the middle of teaching a class. After it passed I had a small black dot in my vision that lasted about a minute and then my vision went back to normal. I am healthy and 60 years old.