I find that swimming is such an amazing way to get the whole body working out. I recently did a swimming class at my gym. It was so much harder than I expected, and I was actually sore the next day. My body definitely got a good work out! I felt like a beginner.
When I used to do step or dance aerobics, sometimes I missed a step. What happens in swimming if you get too fatigued? You could drown! I've always been a bit nervous about swimming. That said, it is an amazing workout. I took a water aerobic class when I was pregant and that was even a killer workout. As as added bonus, I never felt like I was going to drown!
Ha ha ha, I've never heard of anyone who knows how to swim drowning in a lap pool because they got too tired. If you get wiped I'm sure your body'll have enough will to survive that it'll find the stamina to take you to the nearest pool edge. My advice, swim in an outer lane ;)