Firstly: The Ruling of the Sick Breaking his Fast
It is permissible for the sick person to break their fast in Ramadan. This is the overall summarised position.  Scholars have differed over the extent of the sickness which allows for the concession. Consensus has been quoted over this by: Ibn Hazm, Ibn Qudamah, al-Nawawi, Ibn Taymiyyah, al-Zarkashi, and Ibn `Abidin.
Secondly: The Sickness which Intensifies from Fasting
If the sick person fears his sickness will worsen if he fasts, or if it is difficult for him to fast even if it does not harm him, then he may break his fast. This is the position of the majority: Hanafis, Malikis, and Hanbalis.
Thirdly: The Sickness which Harms the Fasting Person and he Fears Dying from it
If the sickness harms the one who is fasting to the extent that he fears death for himself, then breaking his fast is wajib upon him. This is the position of the majority: Hanafis, Malikis, Shafi`is, and a group of the Hanbalis strongly held this position.
Fourthly: Minor Sickness
Whoever is sick with an illness which fasting does not affect and which does not harm him, like light headaches, a blocked nose, or toothache, then breaking his fast is haram. This is by agreement of the four schools of jurisprudence.
Fifthly: The Obligations of a Sick Person Expected to be Cured
If a person breaks his fast from a temporary sickness which he was cured from, then he must make up the days he didn't fast. Consensus has been quoted over this by Ibn Hazm, Ibn Rushd, Ibn Qudamah, and Ibn Hajar al-Haytami.
Sixthly: The Obligations of a Sick Person Not Expected to be Cured
If a person breaks his fast from a permanent sickness which he is not expected to be cured from, then he must feed one destitute for every day he does not fast. This is the position of the four schools of jurisprudence and the majority of scholars.
Seventhly: The Ruling of the Sick Person Fasting Patiently
If a sick person chooses to fast then this suffices him, and this is by agreement of the four schools of jurisprudence.
Eighthly: If a Sick Person Wakes Fasting and is Cured in the Day
If a sick person wakes up fasting and remains so until he is cured during the day, then he may no longer break his fast and he must complete it. This has been explicitly mentioned by the Hanafis, Shafi`is, and Hanbalis.
Ninthly: The Ruling of the Sick Person Withholding if he is Cured in the Day
If a sick person breaks his fast and is then cured during the day, then the scholars have differed over whether he should continue his day abstaining or not. This is according to two views:
The first: is that he does not have to abstain for the rest of the day. This is the position of the Malikis, Shafi`is, a narration among Hanbalis, and the choice of Ibn `Uthaymin.
The second: is that he must abstain. This is the position of the Hanafis, Hanbalis, a position among Shafi`is, and the position of a group of the Salaf.