I think MentalNomad gave some great advice! Rebounding is supposed to be the most effective for cleansing and total body, primarily lymph circulation, as well as cardiovascular circulation. A small amount of time is all that is needed, too. 15 minutes, broken up through the day if desired. You don't have to jump like crazy, either, you can just bounce without taking your feet off of the base. Walking is easy and free. Weights help to rebuild muscle if that is a desired goal.
And somehow, when you exercise, it gives more energy. Of course when you've been ill, that has to be a very little amount indeed (in the beginning) but then you can build up.
I go to the gym feeling sluggish but after I get started I have to make myself stop, and I feel the most energetic afterwards!