One week at Zillow, we were in the middle of an important project (building out our on-demand deployment system), and I got the flu.
My head hurt, my throat was sore, and I needed something to take my mind off of the pain. So I opened my laptop, and started coding. I came back the following Friday with a fully tested and reproducible Jenkins deployment that would be trigger the deployment process.
Sans being sick, having no meetings or interruptions lead to some really productive week. One of the more productive weeks in my career.