What Causes Dizziness And Blurred Vision?

I m a dancer and I am 15. I consider myself very healthy, I do have allergies and I take some medications for that, but usually no other medications are taken besides Ibuprofen (sometimes). My problem is that whenever I am at dance and we have to do backbends (which is where you bend your back as far as you can go while standing), I get a terrible headrush and an awful headache. I often get really dizzy and have pretty bad vision, basically everything in my eyesight just goes away/becomes a red mass. This has been happening almost as long as I can remember, it has just come to a point where I can t do certain dance moves anymore because even though I haven t fallen, I feel like I am going to. This problem also happens when I stand up, not all the time, but when it does happen, it tends to be much worse then just bending my back. I do drink a lot of water and my sleep habits are as normal as they can be (I m a teenager). Is there anything I can do about this? Medication? Exercises? Changes?