Mr. Productivity

Do you ever go through a period at work where you get absolutely nowhere? You might as well have been golfing, sleeping, knitting, or catching up on Lifehacker? And then all of a sudden you have what might possibly be the most productive day in history? That was my day today. I've been working on a project for a few weeks now without getting anywhere. As if a light bulb went off today, I switched gears and accomplished in 9 hours what I would have estimated to take two more weeks given my current pace. I love days like today. Anyone else ever experience this?