I realise this thread was started way back, however since it's been resurrected, I thought I'll add my own contribution based on past experiences.
Back in September of 2014, I wrote a full article on this particular subject, I called it:
Overtraining or under-recovering?
There are certain facts we need to consider here. Prior to the stage we call over training, there are two stages that take place, one on purpose, and one (perhaps) by some miscalculation, stupidity, or both, done by the coach.
As I've alluded to above, there are two stages that precede a state of overtraining, these two stages are called over-reaching, more precisely functional over-reaching, or "FOR" for short (that's the positive stage you want to push your athlete into on certain occasions), and the other being non-functional over-reaching, or NFOR for short, and this particular stage right here, ought to give you a sense of what it is to feel over trained, yet not quite sending you over the edge once all is said and done.
For anyone who's particularly interested in this subject of over-training, please read the full article I wrote (with its link above), and feel free to ask me any question on the subject should you have any.
Thanks.