Sometimes after laying down or sitting for an extended period of time, when I stand up I will feel a pulse in the middle of my forehead spreading throughout my whole head. Then my vision will get blurred. everything will close off into a black circle, until I can only see through a small opening in the middle. after about 10 seconds, My vision will slowly recover. Is this considered a blackout? If not, what would this be considered? Feedback is greatly appreciated! Thanks!