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The following chapter will discuss the various levels of illness that a person may have, and which level of prohibitions may be done in order to help treat them.
Medication in general, even if it involves no Shabbos prohibition in its form of treatment, such as swallowing a pill, is Rabbinically forbidden to be taken on Shabbos unless the form sickness is severe enough to allow it to be taken, as will be explained below within each category of illness. There are however certain forms of medical treatment which are allowed in all cases due to them not being recognized to the bystander as being medication. This matter will be discussed in Halacha 7.
This chapter will discuss the general levels of illness and their respective laws. Chapter 3 will list particular medical symptoms and their respective laws regarding giving treatment on Shabbos!
1. The law of one who has a limb that is in danger but is not in a life-threatening situation:
Having a gentile do forbidden work: All of one’s needs may be done through a gentile, even complete Biblical prohibitions, such as to bake for him or to cook for him if he needs this done.
The prohibition for a Jew to Biblically transgress even when there is a limb in danger: However, a Jew may not transgress Shabbos in doing a Biblical prohibition even if there is danger of [losing] a limb, so long as there is no
danger of life.
The allowance for a Jew to Rabbinically transgress when there is danger of a limb: [However] for a Jew to transgress Shabbos by doing a Rabbinical prohibition [directly] with his hands, such as for example to administer to him any treatment [of healing] which is prohibited due to the decree of [that he may come] to crush herbs, even though that doing so in it of itself involves no remote prohibition even Rabbinically, or even if it itself does involve doing a Rabbinical prohibition in its process, then it is allowed to be done without any irregularities from the way it is typically done during the week if there is a danger of a limb involved even though he is not bedridden and his entire body does not feel sick.
Doing even Biblical prohibitions with an irregularity: [Furthermore] when doing an [action using an] irregularity it is allowed to even do a Biblical prohibition [if it cannot be done through a gentile].
The law of one who has a limb that is in danger but is not life threatening:
Having a gentile do the treatment: All prohibitions needed to be done in order to treat him may be done through a gentile, including even cooking and baking, which presents aside for a Shabbos prohibition, also a Kashrus prohibition.
Having a Jew do the treatment: It is permitted for a Jew to do a Biblical prohibition with an irregularity, although without an irregularity it is forbidden. However, a Rabbinical prohibition may be done even regularly.
Medicine: May be taken according to all.
What is the definition of the danger of a limb?
If there is danger that the limb will no longer function normally if it is not immediately treated, then it is defined as that the limb is in danger even though it will still somewhat function.
In cases that an action may only be done with an irregularity, what is defined to be an irregularity? 
One is to ask a Rav what is considered an irregularity for each particular forbidden action that he must do.
Is a Biblical action not done for its own use considered a Rabbinical action and allowed to be done by a Jew in cases that only a Rabbinical action is allowed to be done?
No. It is considered like a Biblical action being that it appears like one is doing an actual Biblical prohibition. [However, to ask a gentile to do so in cases that only Rabbinical action may be done by a gentile is allowed according to those which hold that it is only considered a Rabbinical action.]
 Admur 328:19
 But the treatment itself does not involve crushing herbs or any other biblical prohibition.
 Ketzos Hashulchan 134 Halacha 4 with regards to one who is bedridden. Seemingly this would apply in this case as well. So also learns Piskeiy Teshuvos 328:15
 Admur 328:19
 Ketzos Hashulchan 138 footnote 18
 Ketzos Hashulchan chapter 134 Halacha 4
 Ketzos Hashulchan chapter 138 footnote 5
 As rules Admur in Halacha 3