I don't know what it was, but my swim last night was great. Maybe I finally managed to get a proper rhythm going or something. I was exhausted after 15laps, but that's respectable enough, I used to swim 1000m a couple times a week, and 15 laps is about 750m. So I'm not that far off.
I've never had the rumoured endorphin rush from exercise, my sister gets it frequently apparently, but I'm very sure she does way more intensive workouts than I do. I've been hyper as hell after a toning class, but with the cardiovascular stuff I collapse before I get past the wall. I'm such a wimp.
Meh, I'm still losing weight at a good pace, so I'm happy.