2) Thus, if there is even a slight chance that the person who fainted is suffering from an illness and is thus in danger, the Shabbos is transgressed to have him evaluated by a medical professional. However, if the one who fainted says that he is completely sure that he is OK and there is no medical evidence or history to suggest otherwise, we do not transgress any melachos of Shabbos to seek medical attention.

3) If a person is bitten by a rabid dog or a venomous snake or scorpion, we transgress the Shabbos to get him/her immediate medical attention. (Shulchan Aruch Siman 328:6)

4) If it isn't known if the dog was rabid or the snake was venomous, it is permitted to trap the animal on Shabbos to determine its status and know the proper methods of treatment. 

 5) If a small child gets locked in a room, and there is no way to get him out without transgressing Melachos (such as breaking the door, using tools, calling a rescuer etc.), we do whatever is necessary to get him out, even if it entails biblical transgressions. (Talmud Yoma 84b. See also Mishna Berura Siman 328 S"K 38) 

6) Even if we can distract the child, talk to him through the door and otherwise keep him calm, Chazal still deemed it Pikuach Nefesh that he may get scared to the point of danger, and thus no such options are considered, and we do whatever it takes to get him out immediately. (ibid.)  

7) Although the Poskim give the age as 6 or younger for how small the child is for whom we must transgress the Shabbos to get him out of a locked room, all agree that if we have reason to believe that he will still be afraid to the point of danger, we transgress the Shabbos even for a child older than 6. (See Shu"t Shevet Haleivi Vol. 8 Siman 75)

 8) If there are multiple ways to get the locked door open, some that will be biblical transgressions and some that will only be rabbinical transgressions, it is best to opt for the lesser of the transgressions, as long as choosing that option won't significantly delay the door being opened.

 9) If an adult gets locked in a room, no melachos may be transgressed to get the door open to allow him to get out. (Unless the situation is one where there is indeed a legitimate concern that this adult's life will be in danger if we don't open the door right away, in which case we treat the situation as if he was a small child. If a nearby Rav is readily available, it is best to consult him for guidance in such a case.)

 10) However, an Aino Yehudi may be asked to get the door open, if the way he does it will only be a rabbinical transgression (such as a rabbinical melacha or even a biblical melacha done in a destructive fashion). The reason for this is that a Shvus D'shvus (an action that is a combination of 2 rabbinical transgressions; being done in a biblically acceptable way and also being done via asking an Aino Yehudi) is allowed in situations of Tza'ar, discomfort. 

 11) One who is embarking on a sea voyage (More common nowadays for those who take cruises) should not begin the journey in the three days before Shabbos, if he will still be on the trip when Shabbos arrives. (See Shulchan Aruch Siman 248:1 

12) The reason for this is that during the first three days of a voyage most passengers are not yet calm and conditioned to the sea atmosphere and will thus have their Oneg Shabbos (Shabbos tranquility) diminished. (See Shulchan Aruch Siman 248:2 that this applies only to salty, stormy waters and not to calm rivers and waterways. Some Poskim posit that nowadays with modern ships, even in salty seas people do not have discomfort during the first three days and thus one may embark on a sea voyage even close to Shabbos. 

 13) Some Poskim maintain that the three days begin with Wednesday, and thus one may only book sea voyages that begins on Sunday, Monday or Tuesday. (See Mishna Berura Siman 248 S"K 4 quoting the Mogen Avraham) 

14) Other Poskim, however, maintain that Shabbos is considered one of the three days, and thus only embarking on Thursday or Friday is an issue, but Wednesday is OK. (Ruling of the Gaon of Vilna, quoted in Mishna Berura ibid.