Sleeping on Rosh Hashanah day:
It is customary to avoid sleeping on Rosh Hashanah day in order to prevent ones “Mazel” from sleeping. Nevertheless, one who misuse’s his time is equivalent to one who is sleeping. [One should therefore not overly indulge in eating and drinking in order so he can use his time wisely.]
After midday: [According to the above-mentioned reason, seemingly one is to avoid sleeping even after midday.] [However] some have the custom to sleep after midday. [This lenient custom applies on both days of Rosh Hashanah, however some limit this leniency to only the second day. Some Poskim rule that this custom is not meant as a public directive, however most Poskim record the custom without any clause. Practically, if one does not feel the need to sleep it is best to avoid doing so on the first day of Rosh Hashanah, even after midday. However, on the second day, there is more room to be lenient. Nevertheless, the above is from a Halachic perspective, however certainly from a spiritual perspective one is to utilize all of his time for saying Tehillim and matters of service of G-d on both days of Rosh Hashanah.]
One is to avoid sleeping on Rosh Hashanah day [even after midday], although some have the custom to sleep after midday. [Practically it is best to avoid doing so on the first day of Rosh Hashanah even after midday however on the second day there is more room to be lenient. However certainly from a spiritual perspective one is to utilize all of his time for saying Tehillim and matters of service of G-d on both days of Rosh Hashanah]
Must one awaken prior to morning on Rosh Hashanah in order to avoid sleeping into the day?
Based on the above, one is to awaken prior to Alos and not return to sleep on Rosh Hashanah day. One is especially to avoid sleeping into the first hour of the day which is the first hour that Hashem sits and judges the world. Due to this it was customary in previous generations for the Shamash to awaken people on Rosh Hashanah about one hour prior to Alos, so they would all be in Shul by the time Alos arrives. Nevertheless, many are lenient today to sleep past Alos, on the basis that the first hour begins from sunrise. Certainly, however, one is to avoid sleeping past sunrise. Even if one is not feeling well he is to place effort to awaken before morning and if needed to sleep only after midday.
May one sleep during the day if he feels exhausted, tired or not well?
One who feels the need to sleep in order to re-energize, may sleep a little before going to shul. Even in such a case, it is best to withhold oneself from sleeping until after midday. This applies even if one has a headache or migraine and the like.
|Sparks of Kabala:
One is to avoid sleeping during Rosh Hashanah day as Z”a is in a state of sleep at this time [i.e. found in a state of Histalkus Hamochin]. However, after midday one is allowed to sleep as Z”a has already awakened through the Tekios blown in Shul. [The prayer and Tekios of each day of Rosh Hashanah affect the drawing down of the Mochin for that day. There is thus no more fear after the prayers have concluded and one is able to sleep.] Rav Chaim Vital related that he witnessed the Arizal, after midday, lie on his bed and sleep. [Practically, however, as implied from Admur, the widespread custom is not to sleep even after midday.]
One who misuses his time:
If one uses his time to learn Torah or pray he arouses his angel above to pray on his behalf. If, however, he goes to sleep then his angel does not pray for him. The same therefore applies for one who does not use his time properly for learning and prayer, as he does not arouse his angel to pray for him above.
 Admur 583/8; Rama 583/2 based on Yerushalmi; Darkei Moshe 583/2; Taz 583/3; M”B 583/9
 See Avodas Yisrael R”H [Koznitz] that it is “forbidden to sleep on Rosh Hashanah”.
 As for why we do not avoid sleeping at night-See Avodas Yisrael R”H ibid that night represents Malchus and on Rosh Hashanah night it is not in a state of sleep.
 Admur ibid; The Rama ibid concludes “This is a good custom”. This is based on the Yerushalmi who states that whatever one does on Rosh Hashanah effects his Mazal. [Darkei Moshe 583/2; M”B ibid] Alternatively, the reason is because it shows laziness. [Bach]
Other Opinions: The Maharam would sleep by Rosh Hashanah [day] just like any other Yom Tov. [Bach 597; Kneses Hagedola 583/6; M”A 583/6; Peri Chadash 583; Elya Raba 583/5] The following Poskim are lenient on this matter as did the Maharam: Elya Raba ibid [“this is our custom even though it’s better not to sleep”]; Levush [completely omitted this custom from the Rama]
 Admur ibid; M”A 583/6; Elya Raba 583/5; P”M 583 A”A 6; Kaf Hachaim 583/37
The reason: See “Sparks of Kabala”
 P”M 583 A”A 6
 Admur ibid; M”A 583/6
 Arizal in Shaar Hakavanos 90a; Peri Eitz Chaim 24/83 [brought in M”A 583/6; Kaf Hachaim 583/36] that the above only applies until midday and the Arizal himself took a nap after Chatzos; Shulchan Gavoa 583/6 [that so was his custom]; Some say that perhaps this was also the custom of the Mahram ibid. [Kaf Hachaim 583/35]
 The reason: See Sparks of Kabala
 Kaf Hachaim 583/36 as after midday of each day of Rosh Hashanah the Hamshacha of Mochin has already been accomplished for that day.
 Shemen Sasson on Shaar Hakavanos ibid, brought in Kaf Hachaim ibid, that even according to the Arizal it should only be done on the second day after midday.
 Mateh Efraim in Alef Lamateh 598/1
 Admur ibid; Siddur Yaavetz; Aruch Hashulchan 583/4; 597/2; Avodas Yisrael R”H [Koznitz] completely permits after midday
 Kaf Hachaim 583/36
 Kaf Hachaim ibid [as the Hamshachas have already been completed according to all by after midday of the second day]; Poskim mentioned in Piskeiy Teshuvos 593/10 footnote 67 in name of Rav Nosson Adler [as the concept of a bad omen taken from the Yerushalmi ibid only applies on the first day]
 See letter of Rebbe Rayatz, printed in Sefer Haminhagim p. 118: One ought to sleep less than usual, intensify one’s devotion in prayer and supplication from the depths of one’s heart, and recite Tehillim at every available moment. Chayeh Adam 139/11; Kitzur Shulchan Aruch 129/20; Mateh Efraim 598/1 that one is to go to Shul and say Tehillim.
 Mateh Yehuda 583 brought in Kaf Hachaim 583/39; Alef Hamagen 584/1; Ben Ish Chaiy Netzavim 11; Some Poskim bring that Rosh Hashanah is one of the five days that one is to awaken early. [Piskeiy Teshuvos 583 footnote 63 in name of Elya Raba] See Elya Raba 693/8; Likkutei Mahrich
 Mateh Yehuda ibid
 Mateh Efraim 584/1
 Piskeiy Teshuvos 583/10
The Chabad custom: I was told by Rav Asher Lemel Hakohen that many are no longer careful to awaken prior to sunrise, as they need energy for prayer, and people today go to sleep later than in previous times. [See Shulchan Shlomo of Rav SZ”A; Mishmeres Shalom 1/1 or the Sefer “Awaking like a Jew” Chapter 2/1] However Harav Leibel Groner, the Rebbe’s secretary, and compiler of Sefer Haminhagim, related to me as follows “Since I was 5 years old my father would wake us on Rosh Hashanah before sunrise in order so we do not sleep at that time.” Rav Eliyahu Landau, the son of Rav Yaakov Landau, [the famed Chassid of the Rebbe Rashab and source of many Chabad customs today] related to me that his father would wake them up at a young age prior to sunrise every R”H and they were very stringent on this matter not to sleep past this time.
 Ben Ish Chaiy ibid
 Chayeh Adam 139/11 [“may sleep a little if he cannot do without it”]; Kitzur Shulchan Aruch 129/20; Ben Ish Chai Netzavim 11 [“If one has a headache or other ailment which forces him to sleep by day he is to withhold himself and sleep after midday.”]
 Ben Ish Chai ibid
 Shaar Hakavanos 90a; Peri Eitz Chaim 24/83 [brought in Kaf Hachaim 583/36]; See Beir Mayim Chaim for an explanation of Erech Anpin and Z”a. See the many Mamarim of Rosh Hashanah found in Chabad Chassidus that discuss this topic.
 Machatzis Hashekel on M”A 583/6; Kaf Hachaim 583/37