This Halacha is an excerpt from our Sefer
Diminishing comfort when sleeping:
Sleeping on the floor or with a stone under the head: Some people are accustomed to sleep on the floor on the night of Tisha B’av. Some people are accustomed to place a stone under their head when they sleep. [The Chabad custom is not to sleep on the ground or sleep with a stone under the head (however one is to diminish in comfort, as stated next).]
Diminishing in comfort of sleep: [Even those who do not abide by the above custom] are to diminish their sleeping comfort on Tisha B’av, such as if one normally sleeps with two pillows, he is to sleep with one pillow.
Pregnant women and people who are weak: A pregnant woman for whom it is difficult to have discomfort in her sleep, is not required to abide by any of the above customs. [Likewise, one who is weak is not required to be stringent in this matter and may hence sleep on his bed as usual.]
May one say good night to another prior to going to sleep?
 Michaber ibid; Kol Bo; Chayeh Adam 135:17; Custom of Chasam Sofer
 Michaber ibid; Mordechai; Rama ibid “Some people are accustomed to place a stone under their heads in memory of the verse that states “And he took from the stones of the place” being that he saw the Churban. [ibid]
 Sefer Haminhagim p. 96 [English]
 Rama ibid; Tosafus end of Taanis; Chayeh Adam 135:17; Kitzur SHU”A 124:2
 The Terumos Hadeshen would sleep the opposite way, placing his head where he normally places his feet. [Leket Yosher p. 110]
 Rama ibid; Tosafus Taanis
 M”B 555:6-7 based on Gr”a
 Leket Yosher brought in Nitei Gavriel p. 436; However, see Nitei Gavriel 56:3 who plainly writes it may not be said.
 The Leket Yosher ibid writes that although it may be said and is not included in “Sheiolas Shalom” nevertheless the Terumos Hadeshen did not do so.
 See Nitei Gavriel 56:3 that plainly writes it may not be said.