I was feeling great before a group ride this morning. I went really hard up a hill and at the top there is a gas station. We all stopped there. As soon as I got off my bike I got really hot and my heart was beating hard and slow. I felt dizzy and blacked out for a second. I sat for a couple of minutes then rode back and felt fine all the way back. I was wondering if the reason i blacked out was because i did not cool down before dismounting my bike. Is this a reasonable explanation? I feel fine now.