Not observing Ramadan for medical / weight reasons

What's the status for this case ? A person was ill. Because of his illness he lost lot of weight. He've been hospitalized and then he started a new treatement ! The treatement helped him gaining weight, but it was difficult for him, a fight for every pound. Before the beginning of Ramadhan, the doctor told him that he was under the weight standards of a healthy person (he's under by about 22 pounds) and that he had to gain more weight, to maintain his health and also because his medication's dosage depends on that : if he loose weight, he have to decrease his medication. For that the doctor advised him not to do the *sawm* during the Ramadhan. So he decided to follow the doctor advocation (of course, he gives the *Sadaqa* for each day), but he feels bad about it even if he knows that loosing weight is not preconized for him, not only because it would be a step back physically but also psychologically (regarding the difficulty he had to gain those pounds) So, what's your opinion on this case ?