I had something similar happen to me this past weekend. It was about 9:30 am and i hadn't eaten anything yet. I came downstairs and all of a sudden got REALLY dizzy. I sat down with my head between my legs and thought for a while that i was going to pass out. Luckily, I didn't pass out but after the episode was over, i was covered in sweat. I also had a really tight feeling in my lower abdomen for the rest of the day. I was nervous and called my midwife. She didn't really have any answers for me. She said it could have been due to low blood sugar since I was late to eat breakfast. She also said that sometimes it is due to a drop in blood pressure. She told me to relax for the rest of the day, eat lots of protein, and to call her if i had another similar episode. I haven't had one since.
I hope you are feeling better. I am not sure what causes this but my midwife didn't seem too concerned. I had eaten lots of sugar the night before (very unusual for me) and hadn't had much protein for dinner. So, maybe it has to do with diet?????