What causes dizziness, headaches, and blackouts on standing?

Hello doctor,

I am a 19-year-old female. Almost every time I stand up or sit up I get extremely dizzy and lose all eyesight, and everything looks like a tv that lost signal. I also lose most of my hearing and there is also ringing noises in my ear. After a few minutes I can see again, but I get about 20 seconds of an excruciating migraine. I usually have to hold on to something, because I almost always lose balance. There have also been a few episodes while just sitting down, I get blackouts. It is just the same as described in the ones when I get while I stand up, but about 20 times longer and I constantly fall and cannot stand or see absolutely anything in those cases. That episode lasts for about half an hour.

I have had the constant spells when I stand up a few times daily (at least) for the past couple of years and thought they would decrease by now, but the bad spells that I get have become more frequent in the past few months, once every two weeks or so. I have not had any injuries in the past few years, so I have no clue what could be going on. It is starting to really concern me. Also, when I am exposed to the color white or yellow my color in my vision changes and I start to see different colors. I have no idea if that is related but I have had those for years.