The Rebbe Rayatz, Rabbi Yosef Yitzchak Schneerson, was the sixth Lubavitcher Rebbe. Born to his father, the fifth Lubavitcher Rebbe, Rabbi Shalom Dov Ber in 5640 (1880), Rabbi Yosef Yitzchak worked tirelessly to keep Judaism alive in the Soviet Union and was jailed for his heroic efforts. Forced to leave Russia, he continued to conduct the struggle from Latvia, and then from the Warsaw Ghetto, eventually escaping the Holocaust to the United States. By the time of his passing in New York on the 10th of Shevat 5710 (1950), he had built the foundation for the global renaissance of Jewish life in the US and throughout the world.
During the last years of the Rebbe Rayatz’s life, his secretary, Rabbi Moshe Leib Radstein, would be at his side when people would enter his room for yechidut (a personal conversation with the Rebbe). The years of suffering, hardship and particularly the torture that he had suffered in the Soviet prison had taken their toll on the Rebbe, and it was difficult for him to speak, making it even more difficult for his listeners to properly understand what he was saying. Rabbi Moshe Leib, whose ear was accustomed to the Rebbe’s speech, would explain the Rebbe’s words to his listeners. Apparently, the source of this story is Rabbi Moshe Leib, himself.
Yechidut, as it is normally used in Hebrew refers to speaking privately with another person. But chassidim explain that the word yechidut stems from the word yechidah meaning, “the singular one”—referring to the highest of the five levels of the soul. In this meeting, the yechidah of the soul of the chassid connects with the yechidah of the soul of the Rebbe.
This story took place when the Rebbe Rayatz was already in New York. A chassid entered his room for yechidut, and woefully related to the Rebbe that he had been diagnosed with a malignant growth. The Rebbe told him that he should go see a great and expert doctor. “But I am at the great doctor right now!” the chassid replied.
The Rebbe’s face changed and with great difficulty, he turned his face to the window on his left, looked up at the heavens and blessed the chassid.
The chassid immediately felt that the illness was gone. And sure enough, the doctors found no more evidence of the illness in the tests that they did. As is said, “The Rebbe removed the illness with his hand.”
When the Rebbe looked up at the heavens, he was actually awakening compassion from heaven. Compassion is the inner dimension of tiferet, (beauty), which is the sefirah associated with healing. This is a message that can be adopted by all: we must have compassion for others and awaken compassion in heaven, thereby drawing down healing for them. 
Rebbe Nachman and the Rebbe Rayatz
In this story, the wise chassid says that the Rebbe himself is the greatest doctor. “Why is the Rebbe sending me to find an expert doctor? The Rebbe is the greatest doctor!” In his book, Likutei Moharan, Rebbe Nachman said that in order to rectify the soul, one has to go to the greatest doctor. He was referring to himself.
It is told that, at least on one journey, the Rebbe Rayatz took Rebbe Nachman’s book, Likutei Moharan along with him.
Once the Rebbe Rayatz journeyed to Poland—apparently to Warsaw—and many Jews came to see him to request his blessing. These were not Lubavitch chassidim, but general chassidim or ordinary Jews living in Poland. When most people go to a rebbe for a blessing, they request material good, be it children, health, livelihood, and the like. This was the case for 99.99% of the people who came to the Rebbe in Poland.
Finally, one chassid came to the Rebbe Rayatz with strictly spiritual requests: that he should have peace of mind to learn Torah, that he should merit to pray with focus, etc. Impressed, the Rebbe Rayatz asked him who he was and who was his rebbe. He answered that the was a Breslover chassid, a disciple of Rebbe Nachman of Breslov. The Rebbe opened his travel bag and showed him that inside was Likutei Moharan, authored by Rebbe Nachman of Breslov, from which he was learning…
 This story was related by Reb Avraham Mayor.
 Likutei Moharan 1, 30:2.