Ellie,
The sentiments you're expressing seem to be going around... I have a client who is having a week just like yours, I'm having a week sort of like yours (though to be fair, not nearly to the same degree), I just got a call from a friend of mine in CA going through a much tougher-than-expected transition at a new job, I have a meeting tomorrow with a struggling grad student who failed both his summer classes, I have a different client who called me for a meeting because a "no-brainer" decision he made last year is starting to bite him in the butt in a major way... coast to coast angst. Maybe Jupiter's in retrograde. Or Mars. Or both.
Teacher to teacher, all I can tell you is that some classes gel and some don't, and it sucks that this one didn't. But that's all that it was, so don't blame yourself... yet. It's not your fault until you have three crap classes in a row--once is a fluke, twice a coincidence. When you hit three in a row, you have a trend, and
then maybe you can start looking inward.
Also, something you might be interested in: inspired by one of my consulting clients, I posted a
blog entry today about the overwhelming feeling of disconnectedness. I think you might find some additional solace in it.
Hang tight.