Hello Today I Was Bike Riding With Some Friends And

Hello
Today I was bike riding with some friends and we decided to stop for a moment by a park. I was already feeling very tired and my head was throbbing but when I got off my bike my vision went crazy. Everything suddenly got so bright, the grass looked neon green and my hand was just a white blur. I sat down for about 2 minutes, nothing changed. I still felt weak also, then I drank some water and after about 5 minutes total my vision went back to normal. Why did this happen?