All the stuff I heard about "more energy, better well-being, you'll learn to love it" are crap.  Everyone I've heard who does some sort of cardio or lifting (gym or not) says how much energy they get right after. And then, there I am, wanting to practically sleep for weeks after I jog for 5 km or swim for an hour. I am completely drained for the rest of the day, even if I do that in the morning. The more often I do it, the more "dead" I am. Thus, there goes my motivation to keep on going every single time I try for a longer period of time.