2. [On Tish'ah B'av], it is appropriate for a person to sleep less
comfortably [than usual] (1). For example, if he is used to sleeping on
two pillows, he should use only one. Some people have a custom to sleep on
the ground and place a stone beneath their heads as a remembrance of
[Jacob's conduct], as [Genesis 28:11] states: "He took from the stones of
the place [and arranged them around his head]." [The Sages comment that] he
had a vision of the Temple's destruction [on that night], and therefore
exclaimed: "How awesome is this place" (ibid.:17) (2). Each person should
follow a practice appropriate to his own level (3).
(1) Pregnant women, and people who are weak or sick, are not obligated to
make themselves uncomfortable in any way (Mishna Berura 555:7).
(2) On that night, Jacob was sleeping on Mount Moriah, the place upon which
the Beit Hamikdash (Temple) would be built in the future.
(3) A person should minimize his comforts and pleasures on Tish'ah B'av to
the greatest extent possible (Rama 555:2). Many authorities prohibit
smoking on Tish'ah B'av; however, since there are those who permit it, one
who is compelled to smoke may do so after midday (halachic "chatzos") in
private (See Mishna Berura 555:8).