I am 18 years old, I am not the most active person. I went to the grand canyon with some friends this summer. We hiked down for a while but we didn't go all of the way down. Going back up I started getting dizzy and took a lot of breaks. On one of these breaks I was leaned against a rock when everything started getting really bright. In a matter of seconds I could only see white. I closed my eyes, people walked by but I could still only see white. It wasn't until someone gave me water and a granola bar that my vision started coming back. I was then able to get up and walk the rest of the way up.
I have been telling myself that is was just dehydration but I would still like to get a second opinion.
I just want to know why this happened. Thanks