The First Surgical Procedure
The Torah gives the following description of G‑d’s creation of Eve:
“G‑d, almighty G‑d, caused a deep sleep to fall upon Adam, and he slept.  He took one of his sides, and He sealed the flesh in its place.”
Why did G‑d have to put Adam to sleep? G‑d could have anesthetized Adam so he wouldn’t feel pain.
Rashi explains that G‑d did not want Adam to see the flesh from which Eve was taken. That could have caused Adam to be repulsed by her.
Every verse in the Torah, while understood simply and literally, also contains profound meaning and a powerful message for us. What is the deeper message contained in G‑d putting Adam to sleep before He fashioned Eve?
Six Days and Six Millennia
We can answer this question by referring to the teaching of Nachmanides that the six days of creation parallel the six millennia since Creation until the Messianic Age, which occurs in the latter part of the sixth millennium, just like Shabbos begins Friday before sunset.
This premise sheds light on the longevity of people who lived in the first millennium. Just as day one of Creation was dominated by the creation of light, the symbol of Divine revelation and infinite kindness, so too the first millennium was governed by G‑d’s infinite kindness.
Most of the action and the most important action of the sixth millennia, however, occurs in the sixth millennium, just as Adam, the “crown of Creation” was created on the sixth day. Similarly, the sixth millennium is when the creation is expected to reach its state of fulfillment and perfection with the coming of Moshiach. The six millennia are like the six days of the week which prepare for Shabbos.
We are situated at the end of the sixth millennium, waiting to enter into the seventh-Shabbos millennium, when the world will rest from all the travail and conflict.
The Creation of Eve
But there is one more step in the creation of humanity; this is the creation of Eve, which required putting Adam to sleep and then separating her from him.  Without this next step Adam’s creation would be incomplete.
Similarly, at the end of the sixth millennium there are two steps that lead the way to the Final Redemption, the Shabbos of history: separation that occurs in a state of sleep and the subsequent reunification.
Before Eve was separated from Adam, Adam and Eve were both full-fledged conjoined human beings, fashioned by G‑d. Although they were united; their unity was a back to back unity. G‑d therefore separated Eve from Adam and then brought her back to him so that they would be united again, face to face.
The same pattern occurs before each Shabbos on a small scale. The mystics considered the time before Shabbos as a time of celestial sleep. To an even greater extent this celestial sleep occurs right before the onset of a New Year on Rosh Hashanah. And on the grandest scale this is the pattern before the Final Redemption.
The Rebbe explained (Toras Menachem 5717) that in the latter parts of the sixth millennium the Jewish people experienced a state of sleep, exemplified by the pain and suffering we endured during the Holocaust and other tragic events preceding the Holocaust.
The Nesira Prelude to Reunification Face to Face
To understand the connection between sleep and suffering we must understand the metaphor of sleep, a period of separation of the soul from the body. When G‑d withdraws His overt presence from the world, the world is said to be in a state of sleep.  When there is a concealment of the Divine we become vulnerable to all the threatening forces in the world. The Torah makes this point explicitly in the Book of Deuteronomy 31:17: “…I will forsake them and hide My face from them. They will be consumed and many misfortunes and traumas will happen to them.”
The state of the world in this time of slumber is also characterized as a period of separation; known in Hebrew and in literature of Kabbalah as the nesirah; which was initiated by the separation of Eve from Adam and serves as an additional metaphor for the pain and suffering of Galus-exile, particularly the last period of history before the Redemption.
However, this separation and state of slumber is a preparation for the time of the reunification of G‑d and His people in the same manner that the original nesirah was a prelude to the reunification of Eve to Adam. As mentioned, prior to the nesirah, Adam and Eve were conjoined, back to back. The nesirah was followed by the reunification of Adam and Eve, but this time their union was face to face. This is the metaphor for the face-to-face revelation and unification of G‑dliness with us, which we will experience during the final Redemption.
Hence the separation and state of sleep is actually a prelude and potential for a much greater union and is to be seen as an integral stage in the unfolding drama of the greatest revelation of G‑dliness in the Messianic Era.
Indeed, the Previous Rebbe, (Rabbi Yosef Yitzchak Schneersohn) characterized the suffering of the Holocaust, as the “birth pangs of Moshiach.” The Previous Rebbe was referring to the words of the Talmud (Sanhedrin) that before the Final Redemption, the Jewish people will go through pain and suffering akin to a woman who goes through birth pangs before she delivers a healthy and beautiful child.
The lesson for us is the knowledge that the period of concealment that we experienced in recent history must be seen as a prelude to the Messianic Age, when the unity between 
G‑d and Israel will be the ideal face-to-face unity.
The Sixth and Seventh Generation
This pattern of the nesira-separation in preparation for the reunification can also be found in relation to the seven generations from the Alter Rebbe (the founder of the Chabad movement) through our generation, under the leadership of our Rebbe.
The Rebbe, in the first Chassidic discourse he delivered upon assuming the mantle of leadership in 1951, cited the Midrash that there were seven generations from Abraham to Moses who brought G‑d’s presence—the Shechinah— into the consciousness of the physical world. In doing so they reversed the pattern of the Shechinah’s withdrawing from the earth to the seventh heaven as a result of the heinous sins committed by seven preceding generations. Abraham began the process of bringing the Shechinah down one level, but Moses through the giving of the Torah at Sinai, and then through the construction of the Mishkan, brought the Shechinah down into this physical world.
This set the tone for the future challenge of making this world a dwelling place for G‑d through our efforts; by observing the Mitzvos and suppressing and ultimately transforming the evil.   
The Rebbe then stated that in preparation for the Final Redemption a new process of bringing the Shechinah down into this world began with the Alter Rebbe, and will conclude in this, the seventh generation, with the coming of Moshiach and the Final Redemption.  
It follows then that the sixth generation, under the leadership of the Previous Rebbe, in which the birth pangs of Moshiach were felt acutely throughout the world, was the generation of the nesira, when the world was in a state of sleep, and Divine concealment. However, this sixth generation prepared us for and contained the seeds of the ultimate unification, to take place under the leadership of our Rebbe in the seventh generation.
Hinted in the Torah
It is fascinating to discover that the verse concerning G‑d putting Adam to sleep and separating Eve from him, the nesira, contains all the letters of the Previous Rebbe’s name, Yosef Yitzchak Schneersohn! Indeed, it is the first verse in the Torah (perhaps the only one) that contains all these letters. It also contains the letters of the words: dor hashishi-the sixth generation, as well as the letters of the word Moshiach and Geulah.  
If the sixth generation is alluded to in the foregoing verse, it stands to reason that the next verse which describes the face-to-face unification of Eve to Adam, represents the culmination of the seven generations, at which time the Final Redemption will commence.
 “G‑d almighty built the side that He had taken from Adam into a woman, and He brought her to Adam.”
In this verse, we can find all the letters of the Rebbe’s name, Menachem Mendel, dor hashevi’i-seventh generation as well as the word Moshiach.
It is also intriguing that each of these verse contain 13 words, the gematria of the word echad-one, and combined we get 26, the gematria of G‑d’s essential name.
The message we can derive from this is that the nesira and the reunification are both manifestations of G‑d’s unity. The difference is that the sixth generation, concealment-nesira unity was concealed, whereas the seventh generation reunification unity will be fully exposed.
It may be further suggested that the above exposition is hinted in three words of the Biblical verse, in Job (41:8): “One is so near to the one.” The Midrash applies this relationship to the two brothers Yosef and Yehudah whose rapprochement portended the future unification of the two Kingdoms of Yehudah and Yosef under one banner of Moshiach. It may also allude to the sixth and seventh manifestations of oneness that cannot be separated.
In this regard, many have pointed to the unprecedented and unparalleled relationship, devotion and bond that existed between the Rebbe and the Previous Rebbe, both of whom represent the ideal of echad-oneness: The Previous Rebbe, whose first name was Yosef, led the Jewish people in the time of concealment-nesira, and the Rebbe who will lead us to the Redemption in the time of total face-to-face reunification.
The above can also be applied to the present, seventh generation period. Within the seventh generation we can also discern two periods. While we are in the final stage of our journey towards the Geulah-Redemption, we also are in a state of nesira concealment because we cannot physically hear or see our Rebbe. However, we have to know that this is but a prelude to the eventual reunification, when we will be reunited with our Rebbe who will lead us to the Final Redemption.