I had heart checked and was perfect 5 years ago I have had ecg a few times since and it was fine. My blood pressure fine and oxygen levels blood tests etc but for some reason some days when I stand up I can go lightheaded sometimes my vision goes a little bit white like white particles until I’m not lightheaded then it goes and then if I sit back down when I’m dizzy my head throbs for a few seconds. What could this be ? I think it’s not bad because all my results are fine ! Should I take multivitamin maybe low iron ?