Divide important tasks into manageable chunks of time. Build in rest periods throughout the day, if it helps you. But avoid working out to exhaustion on a day when you happen to be feeling more energetic. Your strength and endurance is improved by building strength, and getting regular exercise. It may take a couple of days to recover from such a bout.
Deep breathing is a benefit of regular exercise.
Don't forget get some fresh air even if you don't feel up to a workout. Fatigue is tiresome, if you'll excuse the pun, but it can be managed and reduced. Take advantage of some of the techniques in this article to help yourself feel better. Here's hoping you'll be less 'sick and tired of being sick and tired'. It's not the lupus, it's the prednisone.