It is better to follow doctors’ orders now despite feeling 'useless' rather than hurting your body/heart/sternum and become useless for a much longer period if not healed well. Regret won’t help then, but patience will give you good fruits later. You had gone through a major surgery and you do not want to ruin the good results. You compain about little walking and sitting on recliner...this is what you need to do...consider this a time of relaxation!! 
