Was running an 8k today which started at 2. Been hydrating all week and eating right, got 9 hours of sleep last night, ate a light breakfast and some fruit at noon. It was 45 degrees and extremely windy during the actual race. I was trying to hit 28:00 and was on pace for the first mile (5:36). Was feeling solid up, smooth and not breathing hard or owrking hard, until around 1.1 miles in when my breathing became extremely labored and felt like it was limited by my diaphragm, like I couldn't take full breaths. My pace slowed down a ton in the second mile down to around 5:50. I started getting dizzy at 1.8 miles and was making "moaning" noises every time I took a breath. At exactly 2 miles I collapsed into the crowd when my body couldn't go any more. My legs were feeling smooth, my heart rate wasn't up, but I just couldn't take full breaths and my body started to feel beyond tired, I'm guessing as a result. EMS checked me out, all my vitals were completely normal. They said I OVERhydrated and flushed all the electrolytes out of my system as a result. Has this happened to anyone or does anyone have any other theories on what might have happened?