Overtrained?

The last few weeks I've had some difficulty with the workouts.  I'm usually able to make the first and sometimes the second interval power level, but after that I can't make anything.  This morning I made the first interval, but couldn't do the second, so I just did a tempo ride for 30 minutes.  The interesting thing was that during the tempo ride, my HR was really high and I almost couldn't even ride at the power level for 30 minutes.  It may be that my power levels are too high, that I'm stressed, overtrained, or just still recovering from the weekend. 

However, I don't have much stress at all right now and I felt very recovered when I started the workout.  I'm going to take an easy day tomorrow and try again on Friday.  If I fail again, then I'm going to just do tempo workouts on my hard days for a couple weeks and hope that fixes it.  If that fails, then I need to take a week or two off, and forget the cross season and start up slow and easy for the '10 road season.