I did a long run Saturday with my running group, with a goal of 12 miles. I was staying pretty consistent the whole time, stopped for water at 4, 7 and 10 miles (they have water out for us). Miles 1-10 were great, Mile 11 felt really hard, then at the start of mile 12 (both 11 and 12 at an incline), I became so lightheaded I had to sit down. It was like when you stand up too fast and you can't see anything at all, and my hands looked swollen. It was warm but not hot at all, I had breakfast (maybe a little less than normal). I did not feel dehydrated. I slept okay the night before. I stopped for a few minutes then just walked down the final hill (where I usually make up a few seconds!).
At the end of the route, I ate a few orange slices and felt much better. What happened? The only time anything like this has happened was running in 90 degree temps during the summer. I usually run at least 10 miles every weekend, ran my last half 4 weeks ago (and have another one in 3 weeks), and I want to do well and not hurt myself. Could this just be a fluke?