Thread: Light headed and puking

OK - question for anyone who's experienced this:

I do a 18-mile solo ride three days a week where I push mysel pretty aggressively. About 1 out of every three rides I make, I end up getting lightheaded at around mile 13. I back off and regain my faculties, but then at the end of the ride I throw up as soon as I step off the bike and spend the next hour recovering.

So far, I've tried adjusting my diet, and taken myself off of Gatorade during rides thinking the sweetness might be throwing off my digestive system.

Any other ideas on what might be causing this?