What Causes Loss Of Vision, Ringing In Ears And Headache Upon Standing?

I am 21 years old, sometimes (becoming more frequent) when I stand I loose my vision and have loud ringing in my ear. I don t know if it s related but I also get headaches, I call them cold headaches because when I have them it feels like cold air is rushing through my head and it hurts. Any idea what it could be????