That happens to me all the time. It started happening more often a few years ago. I told my doctor and she seemed to think it was not important, since all the tests she did during my last physical were normal. I told my sister and my cousin, who are both nurses, and they said to get up more slowly.

I did some extensive googling some months back and found one or two articles that indicated a possible link to migraines, which kinda made sense for me because the frequency of the problem increased at about the same time that I cut back on the daily meds that I took to control the headaches.

However since the migraines are much less severe and less frequent than they used to be, I haven't gone for a checkup at the neurologist in a long time, so I haven't asked him about it. Also unless it gets much worse, I really don't want to spend the money on lots of tests.

For me it's most likely to happen when I've been slouching or sitting with my feet up, so I try to get up very slowly after I've been sitting that way.