Any idea why I've been having "dizzy" moments a lot more lately?

Before, when I got up too fast, or something like that, I’d become dizzy for a few seconds. I’ve found that for the past month now, doing simple things such as sitting down and having a good conversation with a friend at a table, I can get 5 “dizzy” moments that last a few seconds each time, over the span of an hour.

It’s really strange, I don’t understand why. I haven’t really been doing anything different than before. Anybody have any ideas of why this is happening, or any ways of preventing this from continuing on?

Helpful comments appreciated. =D