I got that sick last winter. I'd had it creeping in for a while, and then one day it snowed hard and my son wanted to go sledding. We made a family trip out of it because my in-laws have a nice hill in their 'hood. Long story short, running up and down the hill blew me away in under 10 minutes. It was all I could to to stand around and everyone else took over hill duty.

Once you get THAT sick you absolutely have to take a day or two of total downtime.