1) The anniversary of the death of one's parent. 2) This is the period of time between sunset and the appearance of three stars on Friday evening. During this time, we avoid doing activities which are forbidden on Shabbat, due to our inability to determine the precise moment that ''night'' (and therefore Shabbat), begins. 3) Since this period of time is not well defined, certain leniencies apply with regards to the rabbinical prohibition of telling a Gentile to perform forbidden activities (See Shulchan Aruch 261:1). It's allowed to ask a Gentile during the twilight period, to perform any forbidden activity (whether Biblical or rabbinical) for any one of the following reasons: a) Shabbat needs; b) To prevent substantial financial loss; c) A Yahrtzeit candle; d) For the sake of a mitzvah.

1) The Sages forbade all forms of medical remedy on Shabbat, because if people saw someone being treated medically, they might think that even grinding up the herbs to make the medication is permitted on Shabbat. Grinding is one of the 39 categories of prohibited creative activity on Shabbat. 2) Applying oil is only forbidden in a place where people apply oil only as a medical remedy. In a place where a certain oil was also regularly applied by healthy people, it's allowed to apply that oil on Shabbat, even if one is using it to alleviate discomfort. This is true because in this case, people will not know that it is being applied due to the discomfort. 3) If a person is considered slightly ill (that is, more than just ''discomfort''), most authorities agree that one may ask a Gentile to perform an act that's rabbinically prohibited in order to help that person; in this case, one could ask him to apply the medical remedy, an act which is rabbinically prohibited for a Jew to perform. See Chapter 90 Law 17.

1) The prohibition only applies to things which are only consumed for medicinal purposes, however, items which are consumed by healthy people, are defined as ''food'' not ''medicine'', and are allowed on Shabbat, even in cases where it is clear that the item is being consumed for medicinal purposes (See Mishna Berurah 328:117). 2) And therefore is defined as ''medicine'' not ''food''. 3) This applies to someone who is only slightly ill, however, someone who is experiencing pain over his entire body, or is ill enough to be bedridden, even though the condition is not life-threatening, may take medicine. 4) Someone who's not sick at all, may have an item that is not generally eaten by healthy people, as long as he's not taking it solely to improve his health (See Mishna Berurah 328:120).