At some point in training, failure is inevitable. So far my biggest failure has been hydration. There have been some days when I have been training in triple digit heat and/or 70% humidity. The next day, I awake to a pounding headache.
Pro tip: if you feel hungover after running, you are dehydrated. This is an especially frustrating challenge. I’ve found that the solution is to fill my water bottles with gatorade, even for the short runs, and to drink gatorade the morning after a hot day of running. Will found a giant tub of gatorade powder in the fruit punch flavor at Harris Teeter. I’m pretty sure it’s keeping me alive right now.