I have had this happen around 4 times in the last few months. I would bend over then when I stand up I get a fluttery feeling with a rapid heartbeat and shortness of breath which lasts a few minutes. Usually if I have a glass of cold water it settles again. Its quite scary even though it is most likely harmless. I think I'm reasonably fit as I exercise sometimes. Does not help my anxiety :( Does anyone else get this ? Maybe I should get it checked out.