at my first football practice of the year, we started off with 100s. the coach said to go all out, and they were using this drill to gauge who the players with speed are. I ran all out, and came first or second. However, there was more than just one sprint; a lot more. I went all out, but by sprint 4 i was spent. I just dogged it from there, just keeping in the front/middle pack. My legs were dead, and i was completely out of energy. At the water break my vision got blurry and 'sparkly' and i had a massive headache and dizziness. so i went to the trainer and got sent home. i don't know what happened at practice after the sprints, but i do know it must've looked really bad for me to leave after like 30-45 minutes. How should i sort of 'redeem' myself after wimping out on day one? and also how hard should i go during practice, because i know for sure 100% is impossible to maintain for long.