you can just walk as much as you can even if it is for few steps here and there. You can exercise in bed. You can do lots of stretching and isometrics in bed. Start out slow.
One exercise that is important it called the homolateral crossover. You lift one leg up and the opposite arm up then switch to the other side. If this seems confusing or you feel it is better to lift the same arm and leg up at the same time, then start off that way then after twelve reps switch to the opposite side up and down. Do this very slowly sitting down, lying down or standing up. This should make you feel more energized.