You might also feel nauseous during or after a run because you're dehydrated. Nausea is an early symptom of dehydration . To avoid dehydration, the general rule of thumb is that you should take in 6 to 8 ounces of fluid every 20 minutes during your runs. During longer workouts (90 minutes or more), some of your fluid intake should include a sports drink (like Gatorade) to replace lost sodium and other minerals (electrolytes). And don't forget to rehydrate with water or a sports drink after your run. If your urine is dark yellow after your run, you need to keep rehydrating. It should be a light lemonade color.
Another possible cause of nausea during or after running is that you simply ran too hard and overexerted yourself. One way to avoid this problem is to make sure you are warmed-up before starting an intense run and to run at a pace that you're ready for.

