I'm hardly an exercise expert, but one thing comes to mind, since it's happened to me before. Did you drink lots of water while you exercised?? Sometimes we forget that just because we're in a pool surrounded by water, we still need to keep the INSIDE of our bodies well-hydrated. You definitely do sweat, and if your heart was pumping and you were breathing hard, you were also losing moisture in your breath. So maybe your symptoms were due to dehydration?

Just a thought. Hope you feel better next time, your workout sounds great

Doreen.