The Midrash (Esther Rabbah 10:1) explains that Achashverosh was certain that the reason he was afraid of an assassination attempt was because he had overlooked rewarding somebody. Indeed, they found the incident earlier (Esther 2:21) when Mordechai warned the king about Bigsan and Seresh’s assassination attempt.
M’lo HaOmer points out that it is a miracle that, although Achashverosh wanted to sleep, he asked to be read a record book which would seemingly have the opposite effect. After all, he was the king, and affairs of state, regional power struggles, palace intrigue, and other similar events recorded in such a record would more likely excite the king instead of put him calmly to bed.
Yosef Lekach writes that the entire records book was simply a list of the king’s personal debts.
Ibn Ezra, however, states that the book was a list of vows, and the king was feeling guilty and was under the assumption that his insomnia was a punishment for an unfulfilled vow.
The Malbim writes that Achashverosh was frustrated about what Esther’s request might be. Therefore, he asked for the records book to investigate if Esther’s request might merely be for him to reward someone for a favor done for him.
According to the Vilna Gaon, the verse is discussing two separate books – a chronicle of the nation’s entire history, and records book of the king’s personal enactments. Similarly, the Malbim points out that the big book is a public book, available to all the citizens. The smaller book is private, and only available to the king. As we shall see (be”H), the difference is that one is more likely to be manipulated.
Me’am Loez writes that this was the first time Achashverosh felt anything like insomnia, and he was therefore greatly concerned. Since this strange, out of the ordinary event transpires in this verse, perhaps this is the reason for the custom (Shulchan Aruch, Orach Chaim 690:15, Mishnah Berurah 690:52) to read this verse in a unique tune1.
The Midrash writes that Achashverosh had trouble sleeping because he was afraid Haman would try to kill him.
R’ Rephael Shapiro of Volozhin wonders why the crux of the Purim miracle hangs on this seeming lie; after all, Haman was not planning on killing the king at this point. He answers that Achashverosh saw in his dream that Haman wanted to kill Esther’s husband. What he did not know was that Esther’s actual husband was not Achashverosh, but Mordechai.
Since every reference to the “king” is really a reference to the King of Kings – H-Shem – the Midrash (Esther Rabbah 10:1) continues that H-Shem was “awakened” from His throne of Glory. How could H-Shem, who neither sleeps nor slumbers (Tehillim 121:4) have been sleeping? The Midrash explains that H-Shem can be said to be “sleeping” when the Jews are not living up to the standard set for them, as it says elsewhere in Tehillim (78:65). Torah Temimah explains that H-Shem ignores our needs sometimes, and only prayer and repentance can “awaken” Him.
The Talmud (Megillah 15b) cites an argument about which king’s sleep was disturbed. The first opinion says it was H-Shem’s “sleep.” The second opinion is that the sleep of both the upper world and the lower world was disturbed. The third opinion is that it was Achashverosh’s sleep, and that it was due to his concern over the nature of the relationship between Esther and Haman, as she had intended by inviting Haman to her feast (see below). Achashverosh thus becomes concerned that nobody seems to be saving him.
Interestingly, Rashi uncharacteristically quotes both the miraculous and natural interpretations of this verse. R’ Avigdor Bonchek writes that Rashi does so to emphasize that the main theme of Megillas Esther is that the true, miraculous nature of things is constantly concealed within seemingly everyday events. Maharal points out that this can be seen in the verse’s choice of calling Him/him “king” without mentioning Achashverosh’s name. If the verse is discussing H-Shem, it is fitting to call Him King. If the verse is discussing Achashverosh, it must be that he was concerned about kingly, political affairs.
Furthermore, Maharsha notes that any instant in TaNaCh in which someone’s sleep is disturbed, the next verse explains the reason. For example, when Yaakov had a dream about the ladder, the next verse (Bireishis 28:10) explains why. Also, when Pharoah had his prophetic, confusing dreams about cows, the next verse (Bireishis 41:1) explains the reason. This verse’s lack of explanation leads one to conclude that something else is going on – namely, H-Shem’s “sleep” is also being “disturbed.”
Based on the fact that the root of “nadidah” (“shaking”) is “nada,” R’ Mendel Weinbach points out that the verse’s use of two letter daleds indicates that there were two disturbances – one in the Heavens and one on Earth. The Midrash Abba Gurion writes that the angel, Gavriel, kept Achashverosh awake telling him, “do good for the one who did good to you.”
The Ben Ish Chai writes that “nadidah” can be read as “nadad Hey,” or “H-Shem Stirred.” He writes it can also be read as “fifty (gematria of the letter nun) dadah.” Since “dadah” can be seen as the root of “edadeim” (“movement”) in Tehillim (42:5), Ben Ish Chai writes that fifty moved Achashverosh. Specifically, he quotes the Ari Z”l that the first verse in Shema contains twenty-five letters. Since we typically say Shema twice every evening and twice every morning, these fifty letters (twenty-five letters repeated) Mordechai was saying came to protect Mordechai. These fifty letters saved Mordechai from the fifty amos of the gallows Haman prepared, zeh l’umas zeh.
1 The classically given answer for this custom is because this verse is the one in which there is a turnabout – when obviously good things are in store for the Jews.