Today,while Standing,my Legs Just Collapsed And I Fell To The

Today,while standing,my legs just collapsed and I fell to the floor. There was no pain or warning and the feeling came back within a minute. I have had lower back surgery, 20 years ago, because at that time I would get a stabbing pain in my back and my legs would give out on me. There was no pain today. Should I see my doctor or just wait and see if it happens again?