I thought about this thread (on the ride home from work, naturally). This happens to me also, and I also get that "something must be rubbing on my wheel" feeling. My suggestion is that if one doesn't want to take a day or two off the bike, then take your next few commutes and really focus on riding much slower than normal. I mean a lot slower...ride like a little old lady. What I've found is that riding the same route over and over results in a kind of repetitive boredom in which I stop noticing the ride, and only think about getting to work as quickly as possible, the meetings I have to go to, my projects, etc, so I wind up riding with a fair amount of intensity without noticing and just wind up in a daily rut. I've also found that if I cut my intensity in half, I only ride a little bit slower. Likewise, if I'm trying to get there in a hurry, I have to go to great efforts just to get there a few minutes earlier. Basically, perceived effort and actual speed results are vastly disproportionate. So my suggestion to anyone hitting this commuter's fatigue is instead of taking a day or two off, just start budgeting an extra five or ten minutes for your commute and really relax on your rides. In a few days you'll feel like ramping up the effort again.