I'm not sure what this is...

Sometimes whenever i'm alone, i'll be walking and all of the sudden my vision starts to have black spots. A few at first but they collect and soon i can't see anything but tiny black dots. I start to feel dizzy, but then i see the black dots come together and start moving, like actual bodies that are moving around me. And then it'll just go away and i'll feel normal again.
I asked one of my wiccan friends if she knew anything about it and she said i might be drifting into and then out of a different plane. I just want to know what is happpening is all.