Dizzy After GENTLE Swimming?

I just got out of the pool from about 15-20 minutes of gentle swimming, some butterfly strokes, some frog leapish moves, paddling along, but then I start feeling dizzy and lightheaded near the end, so I get out and I nearly fall over, trying to put on my shoes. It felt like the world was spinning and I'm still having a little of that now. I heard stuff about taking in to much chlorine or something and dying, and now I'm super paranoid. Please help!