The reason you sometimes feel like you've gotten better after taking a break is because the muscles in your arm, wrist, and hand have had a chance to recover. If you play guitar everyday, your arm and hand are always fatigued whether you realize it or not. After I'm drilling speed exercises for an hour or two, and I try to hold my fretting hand open, sometimes I can't; and my fingers will start moving on their own, it's weird. But it's just fatigue. So like any work out, you want to schedule some recovery time, which is hard because playing is addicting!

~Rusty