How do general fiqh rulings apply to people who fall under exceptional categories?
Question
How do general fiqh rulings apply to people who fall under exceptional categories? Do they change, remain the same and require expiation etc. What I mean specifically is for a chronically ill person experiencing not an acute illness but rather an extended/ing debilitating illness; how would regular rulings apply to them? A previously healthy, practicing person rendered unable to perform many functions due to severe weakness/pain/dysfunction stemming from illness. They are not able to for example - extend efforts to perform sunnah hygienic practices such as shaving the underarms and pubic hair in due time, they find difficulty in performing prayers regularly and consistently, reading and reciting is difficult so cannot maintain habit of worship.
Answer
All praise is for Allah and there is no tawfiq or good except by Him. So long as a person has a sound mind, then they are obligated to perform what is fard or wajib and abstain from what is haram, except in cases of dire need, such as when their life or limbs are in danger. A person in the situation you described does not have to perform sunna actions such as removing the hair from under the arms and in the pubic area. If they are unable to fast due to a chronic illness they do not anticipate getting better from, they can pay the fidya instead. In terms of salat, they must seek assistance, even if it means hiring someone, to fulfill obligations that they cannot perform on their own, such as wudu or ghusl.
In summary, such a person should focus on fulfilling what is obligatory, even if it means praying a prayer with just the integrals or while sitting down if they cannot stand or laying down if they cannot sit. They must seek assistance for the actions they cannot do on their own. They can add sunna actions whenever they have the strength and ability to do so. A person in such a condition should also have a good opinion of Allah, and remember that their worship of Him attracts mercy, forgiveness, baraka, and all good to them. Allah knows best what is correct.