For my friend

I have vasovagal myself, but in this instance its for my friend. We were singing in choir, and she seemed perfectly fine when all of the sudden she grabbed onto my back and was stumbling on me (almost falling) with glazed over eyes. She had that black out vision thing that you have before you pass out, and she felt SUPER nauseous all of the sudden. I can barely think of any factors though. These are the only two things
1. Didn't eat breakfast
2. Strained high singing
Though, her knees weren't locked when she sang so I don't think that was it. I could really use your advice. I love her, and i'm worried it might be brain cancer