I'll be active and moving around the house, after toilet. Suddenly when I sit on the sofa, feel mildly dizzy. Oximeter reading shows pulse -90-95, saturation O2- 98%. After sitting on the bed for two minutes, feel sleepy. Sleep is a nap for 30 minutes and then wake up to have some food. It's really strange how I feel mildly dizzy post bowel movement,if I sit suddenly. Is it something related to heart functioning? My ECG, echo was done 2-3 months back during annual check up and was normal. But I had episodes of sinus tachycardia due to gall stones. Does it need more investigation?