I Am A 66 Year Old Woman. I Recently Fainted

I am a 66 year old woman. I recently fainted while sitting at the dinner table. I suddenly felt full and nauseous then I couldn't hold my head up and blacked out for approximately 30 seconds. I had broken out into a cold sweat & family members who picked me up said my coloring was ashen. I had recently been experiencing swelling of legs and ankles. What could have caused this& is there cause for concern?