Crying Due to Illness
Answering the question: Is crying due to illness considered a form of ungratefulness to Allāh?
The eye sheds tears and the heart grieves, yet we do not say anything except what is pleasing to our Lord.
Related by al-Bukhārī
[Q]:I am ill and I sometimes cry because of what happens to me after my illness. Is this considered an action which opposes Allāh and of not being pleased with what He has decreed? I do not do this action willfully. Likewise, does that ruling also include talking to my relatives about my illness?
[A]: “There is no harm in crying, if it is simply tears coming from the eyes, without wailing. This is based upon the statement of the Prophet (ṣallallāhu ʿalayhi wa-sallam), when his son Ibrāhīm passed away: “The eye sheds tears and the heart grieves, yet we do not say anything except what is pleasing to our Lord. By your death - O Ibrāhīm - we are indeed in grief.”  The aḥādīth with this meaning are numerous.” 
 Related by al-Bukhārī (no. 1303) and Muslim (no. 2315), from Asmāʾa ibnt Yazīd raḍī Allāhu ʿanhā.
 Fatāwá al-Mar‘ah (p. 12)