To preface this, this isn't a cop out or an explanation to people as to why I have quit fitness, so don't worry ;)
I recently took a 'step down' in intensity level of my workouts. Perhaps that is a bad way of putting it... I actually cut 3 hours a week of working out (down to about 10 now so ~10-12 workouts a week from 15). I had been feeling for a while that my physical endurance has been suffering due to lack of recovery time for my muscles but I kept pushing myself mentally to keep going - I was (and, well, still am) scared that I will plateau.
But this week the physical exhaustion spilled over to my psychological exhaustion and I began feeling tired when I would usually feel energized and, for the first time in months, began dreading working out. This change in my mentality surprised me (especially seeing as endorphins give you a high well after you stop exercising) but I was not willing to just all out stop. If you're interested in my workout schedule there is a picture of it below. Anyhow, I decided to just back off from my P90X workouts and still continue with my Insanity workouts (as the P90X workouts were just added to prevent plateauing anyways, though it wasn't likely that it was going to happen).
After two days I seriously cannot believe the change in my outlook! The sun is brighter, air more fresh and even the concrete in Toronto looks cleaner! It seems I had started to run into overtraining my body, and it is a good thing I was listening to my body telling me to slow down. Comparing my energy levels from last week to this week, it seems that they have doubled, even though I have the same caloric intake every day! I'm not sure if it had something with the increased amount of cortisol (a stress hormone) that I would produce during my second or third workout of the day, I can only guess, but I am glad that it has stopped for now =)
Moral of the story is: Listen to your body! Make sure you take rest when you need it, eat enough calories to reduce or eliminate muscle loss while training, sleep 7-8 hours a night and just remember that if you overtrain for a long period of time it can take MONTHS to recover!