When dealing with an illness, Muslims are advised to seek medical attention. According to the Prophet Muhammad (peace and blessing be upon him), "Seek medical treatment, for Allah has provided a cure for every illness." (Abu Dawud)
They are also encouraged to pray too, using certain prayers (du'a) to call on Allah to heal whoever is sick. These supplications can be found in Holy Books like the Quran and the Sunnah, a compilation of the sayings and teachings of the prophet.
Du'a for healing sickness
These prayers include:
1) "Allahumma rabba al-nnas adhhibi al-ba'sa ishfi anta al-sshafi la shifa'a illa shifa'ula shifa'an la yughadiru saqaman."
(O Allah, O Lord of Mankind, remove the affliction and send down cure and healing, for no one can cure but You; so cure in such a way that no trace of illness is left).
2) "As'alu Allaha al-zheem rabba al-'arshi al-azheem an yashfiyane."
(I beseech Allah, the Great, Lord of the Mighty Throne, to heal me).
ALSO READ: Du’as for seeking knowledge
3) "A'udhu bi izzati Allahi wa qudratihi mimma ajidu wa uhadhiru."
(I seek refuge and protection in the August might and power of Allah from the pain and illness I am suffering from and I'm afraid of).
4) "An-nee mas-sa-ni-yaD-Dur-ru wa 'AN-ta 'Ar-Ha-mur-raa-Hi-meen" - Quran 21:83–84
(Truly distress has seized me, but You are Most Merciful of those that are merciful.)
The Sunnah adds that suicide is never an option for a Muslim no matter how ill or sick he/she feels.
"None of you should wish for death because of a calamity befalling him; but if he has to wish for death, he should say: "O Allah! Keep me alive as long as life is better for me, and let me die if death is better for me," the Prophet Muhammad advises.