Fainted

Last night I was watching a movie with my fiancé when I felt really thirsty, so I got up to get some water and when I got to the cabinet to get a cup my eyes rolled into the back of my head and I could not move or talk, luckily my fiancé walked in in time to catch me and help me as I went to the floor, he gave me some water and juice and I was fine after a few minutes, was wondering if anybody else has had this happen to them and if they know what might have caused it?