Vision fades, i feel really weak and usually fall to my knees, followed by pounding headache lasts 30 seconds?

This happens a LOT to me. It used to just be maybe once a month, now it's sometimes twice a day. Sometimes it's when i stand up, sometimes it's when i stretch my back, and sometimes i'm just already standing up and it happens. Generally it starts with my vision fading to like a black or green and then i feel really weak and collapse usually to my knees or the ground. Then right after i get my vision back i get a painful sharp pounding headache. All of this combines only lasts about 30 seconds. I don't always collapse, sometimes i just lose the vision and feel really weak. It scares me a little. My mom always said i'm probably just getting overheated, because i do get overheated easily, but i don't think it's that. Sometimes it happens in the shower, and that time i think it might be overheating, but i'm not always hot when it happens. Although that's what i'm mainly worried about, i'm also very tired a lot. I'm a dancer, so i'm used to soreness, but usually i'm excessively sore after classes. Specifically, i have a lot of back pain. I also get out of breath much mre easily and have trouble concentrating. I get headaches a lot. I haven't lost any weight, had any appetite loss, no stomach issues outside of cramping(but usually just for my period) just to be clear about that. Anyway. Any ideas?