Why stay up all night Shavuos

I saw an interesting midrash* the other day. My screen capture isn't working, but here is a rough translation.

In the days leading up to Mattan Torah, Moshe told the Israelites to prepare themselves:

טו  וַיֹּאמֶר, אֶל-הָעָם, הֱיוּ נְכֹנִים, לִשְׁלֹשֶׁת יָמִים:  אַל-תִּגְּשׁוּ, אֶל-אִשָּׁה.

15 And he said unto the people: 'Be ready against the third day; come not near a woman.'

and his preparation was to prepare themselves {ritually} in terms of purity. But the Israelites prepared for that third day by staying up all night learning the laws of Shabbat and Parah Adumah which they had received at Marah. As a result, when the time came for Mattan Torah, they dozed off. And Hashem woke them with great thunder and lightning, as it says:

טז  וַיְהִי בַיּוֹם הַשְּׁלִישִׁי בִּהְיֹת הַבֹּקֶר, וַיְהִי קֹלֹת וּבְרָקִים וְעָנָן כָּבֵד עַל-הָהָר, וְקֹל שֹׁפָר, חָזָק מְאֹד; וַיֶּחֱרַד כָּל-הָעָם, אֲשֶׁר בַּמַּחֲנֶה.

16 And it came to pass on the third day, when it was morning, that there were thunders and lightnings and a thick cloud upon the mount, and the voice of a horn exceeding loud; and all the people that were in the camp trembled.

and vayecherad indicates startling and sudden waking from slumber. Just as {we see by Ruth that} it is written:

ח  וַיְהִי בַּחֲצִי הַלַּיְלָה, וַיֶּחֱרַד הָאִישׁ וַיִּלָּפֵת; וְהִנֵּה אִשָּׁה, שֹׁכֶבֶת מַרְגְּלֹתָיו.

8 And it came to pass at midnight, that the man was startled, and turned himself; and, behold, a woman lay at his feet.

and then again, at Maamad Har Sinai, they repeatedly fell asleep, only to be awoken time and again, as it states:

יד  וְכָל-הָעָם רֹאִים אֶת-הַקּוֹלֹת וְאֶת-הַלַּפִּידִם, וְאֵת קוֹל הַשֹּׁפָר, וְאֶת-הָהָר, עָשֵׁן; וַיַּרְא הָעָם וַיָּנֻעוּ, וַיַּעַמְדוּ מֵרָחֹק.

14 And all the people perceived the thunderings, and the lightnings, and the voice of the horn, and the mountain smoking; and when the people saw it, they trembled, and stood afar off.

Therefore, nowadays on Shavuos night, we reenact this exemplary behavior of the Israelites. We stay up all night learning, and then fall asleep while standing on our feet, during Kriyas HaTorah, during the reading of the Aseres Hadibros. And yet, despite this, our hearts are directed towards our father in heaven, as it states:

ב  אֲנִי יְשֵׁנָה, וְלִבִּי עֵר; קוֹל דּוֹדִי דוֹפֵק, פִּתְחִי-לִי אֲחֹתִי רַעְיָתִי יוֹנָתִי תַמָּתִי--שֶׁרֹּאשִׁי נִמְלָא-טָל, קְוֻצּוֹתַי רְסִיסֵי לָיְלָה.

2 I sleep, but my heart waketh; Hark! my beloved knocketh: 'Open to me, my sister, my love, my dove, my undefiled; for my head is filled with dew, my locks with the drops of the night.'

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Footnotes:
* Alright, I'm kidding. I made this up.