How is it determined that patients are exempt from fasting?
How should fasting be evaluated when it comes to illness? What are the general rules?
It is not 'illness' that allows not to fast; in the case of fasting, 'delayed healing' or 'increasing sickness' is a disease that allows not to fast. It can be understood from this that it is permissible not to fast in case of illness, which results in the prolongation or further deterioration of human health.
If the disease is a disease that cannot be cured, the patient does not fast. S/he gives a fidyah to the poor for every day s/he can't keep.
If there is a situation that will not harm him/her despite his/her illness, s/he will fast, s/he is not allowed.
It would be makruh not to use such a license, that is, to fast despite the hardship, if s/he will suffer from his/her illness and be exhausted. The problem here is not a headache either. For example, it is a case of blindness due to low blood sugar.
If there is a condition that will worsen his/her illness if s/he fasts, then fasting may even become prohibited. It is necessary to protect the health trust of Allah.
The patient's decision about fasting can be determined by the patient's own experience, whether it is harmful or not. At this time, it is better to determine it by consulting a specialist doctor.