Nausea and exercise

Has anyone experienced nausea after excerise?  Every day I swim I feel mild to moderate nausea that evening (5 times in 12 days)  I'm pretty sure it's not dehydration because I'm very carefull to drink at least half my daily fluids before I start swimming and finish up the other half in the early evening.   If you are aware of a connection please fill me in and any suggestions to curb this issue would be appreciated. 

Stupid me searched for an answer after posting this question.  Answer: I'm not crazy and there is a way to prevent it.  Eat some carbs like oatmeal before execise.  Thanks for looking