Why Is It Forbidden to Wake a Sleeping Person?—Jewish Prohibitions of Our Grandmothers
"Gezel Sheinah" —stealing sleep.
This expression is used when someone wakes another person without a compelling reason. The Chafetz Chaim said that stealing sleep is a more serious offense than “ordinary” robbery, because a person who steals an object can repent and return it to its owner, whereas stolen sleep cannot be returned.
The book "Me'orot HaGedolim" (Rabbi Yisrael, 90) cites a statement by Rabbi Yisrael Salanter that stealing sleep is forbidden by the Torah.
However, some maintain that the expression "Gezel Sheinah" (stealing sleep) is not entirely precise, since the word "gezel" (robbery or theft) may be used only when referring to the theft of an object. The prohibition against waking another person without a compelling reason is based on the Torah prohibition “Do not wrong one another” (Leviticus 25:17). From this, the prohibition against causing distress to another person is derived. In addition, one who wakes another person without a compelling reason violates the Torah commandment “Love your fellow as yourself” (Leviticus 19:18). Rabbi Akiva called this commandment “the foremost principle in the Torah.”
Rav Chaim Kanievsky explains the “limits” of this prohibition (from the book "Derech Sichah", p. 367). Rav Kanievsky was asked the following question: In one yeshivah, a study hall was locked without anyone noticing that one student was still inside. When this became known, it turned out that the student, who had the key, usually slept during the day until the beginning of the next seder (study session). Should he be woken, or would that constitute stealing sleep, which cannot be rectified? Rav Chaim answered: It is forbidden to wake another person, as it is written: “Love your fellow as yourself.” But the person who is sleeping is also obligated to observe this mitzvah. Therefore, he should be woken (for “rescuing” the young man from the locked study hall is also fulfillment of the commandment “Love your fellow as yourself”).
(Rav Reuven Kuklin)
