So I'm cruising down the highway and I look down at the tach and it the needle dropped to zero!!

That freaked me out, I thought the engine stalled out or something, but it felt like the car still had power so I prodded the gas pedal and the needle went right back to where it was supposed to be. It seems to be behaving now (but then again I can't stare down at it all the time)
Has this happened to anyone? Did the needle actuator jam? The signal to the tach hic-uped? Are there bigger problems? (no warning lights came on)
Any other explainations?