S. R. Faruqi:

'Sahib' can be the beloved, or it can mean God; any respected personage at all can be called 'Sahib'. See

{1054,10}.

In the sense of God Most High, a verse by Vaj'hi from qut̤b mushtarī :

jo ṣāḥib sūñ rāẓī hoñ yak dil ache
us āsān hove jo mushkil ache

[if one is wholeheartedly accepting toward the Sahib
that would be easy which is difficult]

In the sense of the beloved, a verse by Momin:

ṣāḥib ne is ġhulām ko āzād kar diyā
lo bandagī kih chhūṭ gaʾe bandagī se ham

[the Sahib freed this slave
look at the servitude-- that we have been freed from servitude!]

In the sense of a respected person, from the second divan:

{775,10}.

In the present verse all three meanings of 'Sahib' are present:

(1) He is saying to the beloved or to some friend, 'In sickness of the heart my life will certainly go, so there's no point in medicine. But if God wishes my health, then I will also take medicine. That is, if my health is desired by God, then my own temperament will be inclined toward medicine. If God does not wish me to become well, then I will not be cured.'

Hazrat Khvajah Nizam al-Din Auliya says that he had in his possession a hair from the auspicious beard of Hazrat Baba Farid ul-Din Ganj-e Shakar that he had wrapped up and kept in a niche in the wall. Whenever he gave that packet as an amulet to some sick person, a cure took place. But sometimes after a major search, the packet was not in its proper niche, and not to be found anywhere, and without the amulet the sick person died. (That is, if the Divine will decreed the sick person's death, then the means of a cure themselves became unavailable.) It's possible that these words of Hazrat Khvajah Nizam al-Din Sahib Auliya might have been in Mir's mind, and the meaning of the second line might be 'If my health is decreed in the Divine will, then I will also take medicine'.

(2) He has said to his friend or well-wisher, 'Although recovery from this sickness is not possible, if you wish it then it's all right, I will also take medicine.'

(3) The beloved has given the grief of the heart, but she also feels some attachment to the speaker. Thus at the speaker's sickness (mortal illness) she also feels grieved. Thus the speaker/lover says, 'All right, if this is what you want, then let it be as you wish; I will even take my medicine'. In the beloved's own sorrow, the point is that the sickness of the heart is a kind of sickness that the beloved herself, even if she should wish, cannot remedy; nor can the beloved's attention or sympathy lessen that sickness. Saqi Faruqi:

ret kī ṣūrat jāñ pyāsī thī āñkh hamārī nam nah huʾī
terī dard-gusārī se bhī dil kī uljhan kam nah huʾī

[our life was thirsty like sand; our eyes did not become moist
even/also through your sympathy, the tangledness of the heart was not lessened]

With regard to all three meanings, but especially the third one, in the verse has a sorrowful melancholy and, through submission to the decree of fate, a dignity. In this way, instead of sentimentality and a superficial turmoil and commotion, there has come to be in the verse a thoughtfulness and seriousness.

The phrase tum kuṛho ho too is fine--since s/he said nothing, and through silence said everything. Especially if the addressee would be some confidant of the beloved's, then kuṛhnā is superbly harmonious/appropriate, since in it is also the interpretation of enduring sorrow in silence. The speaker/lover knows very well that he will not survive ( muqarrarī is stronger than muqarrar , because in it is the sense of 'already decided'; Ghalib has often used vaj'h-e muqarrarī for his Rampur salary/pension). But the speaker/lover feels no sorrow over his own death; rather, his sorrow is that the beloved/addressee is grieving.

The verse has many words that show wordplay with 'sickness', but the wordplay of mizāj with marẓ has a complete affinity. With regard to old Greek/Islamic medicine, a person is a collection of four inclinations or humors. If some humor becomes out of balance, then sickness is the result.

FWP:

SETS
MOTIFS
NAMES
TERMS == WORDPLAY

Note for grammar fans: In the second line, why choose idhar over udhar , when so often the wider-ranging udhar is the richer possibility? In the present verse it seemed to me that 'in this direction' could create a small ambiguity of its own by referring either to 'toward my treatment and cure', or 'toward me' (in the sense of paying the speaker any attention at all).