If you’re really driven, I think you can get into physical trouble before really noticing a lack of desire. For me, it’s when I start getting insomnia really bad, which is a clue that maybe my hormones are out of wack. If I then respond with a couple extra cups of coffee to get me thru my days, keep pushing hard, a little dehydration here and there, and wa-lah: heart problems pop up. Not good. I learned my lesson. Now, if I should be tired but can’t sleep, I take a break from training

We can get nitpicky about terminology, but as a few others have stated, chances of it being 'over-training' are very slim... Chances of 'over-reaching' for us mere mortals is very real. Over-training has lead to the end of their career for many athletes...

So many variables go into triathlon training it's impossible for anyone here to answer your question... Let your body tell you. Learn to listen too it as it will guide you during theses 'down' times... We all get them. Don't feel like doing shit because you feel like shit and lack the internal motivation. So don't do shit for a few days. Don't stop completely, just do some recovery type stuff. If your plan calls for a swim, just go swim a few easy laps. Run? Hey, a brisk walk is awesome... Don't stress about missing a 'training' day here and there... You've got to trust the plan you're on because that's the path you've chosen for this race! That's right, this race. Take notes and learn...