Sure, it might seem like all you're doing is lying around a pool, but with temperatures where they've been over the last few weeks (we're way over the historic averages for temperature and humidity, according to this guy I talked to who lives behind my local 7-Eleven), just lying around is enough to put your body through the equivalent of an intense workout session, which is why you were totally justified in not even bothering to go to the gym once this weekend. Good call on your part!