I lost about 6 weeks to viral pneumonia that hit me in the 2nd week of Jan. surprising how much / how fast you "de-condition" in that time. you really have to build it back up "slow and steady" ... if you get sick again (common w/ mono), you've wasted all the work of getting back to form. My first stage back is to get on the rollers 5-6 days a week, steady, smooth sessions; just re-introduced the rowing machine as well. Cardio comes back on its own when the frequency is high.