Answer: In investigating this condition among my runners, I’ve discovered that the most common reason for this is low blood sugar. In this case, increasing the blood sugar snacks, such as gel products or candy, can provide psychological relief. The general rule of thumb is to consume 30-40 calories per mile, with 2-4 oz. of water, every 1-2 miles. Most find that they need to start taking the blood sugar boosters about 4-6 miles into a long run.
Some of the light-headedness is due to fatigue. By taking walk breaks often enough from the beginning and starting more slowly, this problem can often be managed or eliminated.