Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Brother, we would like to thank you for the great confidence you place in us. We invoke Allah to grant you a quick recovery, ameen.
In fact, you should resort to Allah seeking His blessings and favors to grant you quick recovery. You may ask good people to make du`aa’ on your behalf too. This is, of course, with necessary medical treatments.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
You may use any of the standard supplications transmitted from the Prophet (peace and blessings be upon him); to list a few of them:
Allaahumma rabba an-naasi adh-hib al-ba’sa ishfi anta ash-shaafi laa shifaa’a illaa shifa’uka shifa’an laa yughaadiru saqaman
Asa’lu Allaaha al-`azheema rabba al-`arshi al-`azheem an yashfiyanee
Allaahumma matti`naa bi asma`inaa wa absaarinaa wa quwwaatinaa maa ahyayatanaa
(O Allah, You are the Lord of the worlds; so, remove all of my afflictions and cure me in such a way that no trace of illness is left.
I ask of Allah, Lord of the Great Throne, to heal and cure me.
O Allah, I ask of You to bless me to enjoy my faculties of hearing and sight and energy as long as You allow me to live).
I would urge you to get a copy of Invocation of God by Ibn al-Qayyim al-Jawziyyah; you may find a number of excellent du`aa’s there for all occasions.
Allah Almighty knows best.
Excerpted, with slight modifications, from: www.askthescholar.com