and he worries about his fragile mental state.  So when Lorry asks the ghost if it cares to be recalled to life, it isn’t sure.  Lorry is not sure Dr. Manette will be able to make the transition well, since he is so fragile mentally.

Mr. Lorry, as he travels on the mail train in chapter three of the book, is never quite asleep. Dickens states that the bumping of the coach is always, to a certain extent, with him; he is aware of its bumpings and swayings. However, he does have a sort of half-dream, what Dickens calls "a current of impression," which is obviously connected to the fact of what he is doing and the anxieties that are laying upon him at this moment.

The drift of his "fancy" is that he is going to dig someone up out of a grave. He is not sure who exactly it is that he will be digging up, but he sees various impressions of a person—always a man of about forty-five years of age who has been buried, he says, for nearly eighteen years and has since given up all hope of being dug up. The "spectre" reacts differently when Lorry asks him, in the dream, whether he wants to come up and see "her." Sometimes he says yes; sometimes he doesn't understand who is being spoken about; and sometimes he says no—it would kill him. The creature is then dug up out of its grave. The refrain that the person has been buried "for eighteen years" is repeated throughout the dream.

In Chapter Three, "The Night Shadows," after falling asleep on the way to Dover, Mr. Lorry dreams about Tellson Bank. As the dream develops, Mr. Lorry envisions a man who has been buried for eighteen years, and then manages to dig himself out. Throughout the dream Mr. Lorry revisits this three times, thus confirming that the man was buried for eighteen years. In a reflective moment while waking up, Mr. Lorry contemplates the severity of man being (literally) kept away from nature. This notion is confirmed as Mr. Lorry himself gazes at the vast countryside.

The dream itself is quite telling because it serves as a way for Dickens to explore a key motif throughout the text -- resurrection or rebirth. The dream not only haunts Mr. Lorry, but it also haunts the text on a general level. The plot of the novel is thus driven by this notion of resurrection, at least symbolically, and as Mr. Lorry is resurrected from sleep, we see the sun function as a mechanism of rebirth. 

Mr. Lorry is on his way to meet Lucie Manette and to accompany her to France to meet the father she thought was dead. He sends a message back to Tellson’s Bank (where he is a bank manager) that says simply, “Recalled to Life.” This message of resurrection leads to his dreaming of a disembodied voice speaking to him. Mr. Lorry asks him how long he has been “buried” (meaning, imprisoned in the Bastille), and the voice (Doctor Manette) replies that it has been eighteen years. He had given up hope of being dug out. When Mr. Lorry asks him if he cares to live, Doctor Manette says that he cannot say. Mr. Lorry asks if he would like to see “her” (meaning his daughter, Lucie). Doctor Manette does not answer. This conversation is repeated several times, always with the theme of being dug out of his grave and recalled to life. It is probable that this is not simply a dream but a remembrance of the real conversation that Mr. Lorry had with Doctor Manette when the latter was finally released from the Bastille.

I assume from your question that you're referring to Mr. Lorry's dream in chapter 3, "The Night Shadows." As he rides in the mail-coach, Mr. Lorry "nodded in his place, with half-shut eyes." As Dickens describes,

Though the bank was almost always with him, and though the coach (in a confused way, like the presence of pain under an opiate) was always with him, there was another current of impression that never ceased to run, all through the night. He was on his way to dig some one out of a grave.

This "someone" never becomes clear to Mr. Lorry, though the faces in his vision are "the faces of a man of five-and-forty years" and look ghastly in their "worn and wasted state." Mr. Lorry repeatedly asks this person how long he has been buried for, to which the "spectre" replies, "Almost eighteen years." When Mr. Lorry tells the spectre that he has been "recalled to life" and asks, "I hope you care to live?" the ghost responds, "I can't say."

Next in the dream, Mr. Lorry asks, "Shall I show her to you? Will you come and see her?" and it is here that the dream varies: sometimes the spectre replies, "Wait! It would kill me if I saw her too soon"; other times he says "Take me to her"; or else he is confused, saying, "‘I don’t know her. I don’t understand."

After this conversation occurs, the Mr. Lorry in the dream digs the spectre out of his grave, at which point "he would suddenly fan away to dust" and Mr. Lorry would "start to himself, and lower the window, to get the reality of mist and rain on his cheek." The exchange about the spectre having been buried for eighteen years recurs several times, as well as the spectre's seeming ambivalence about coming back to life.

When Mr. Lorry finally truly awakes, it is dawn, and the "shadows of the night were gone." As the chapter closes, Mr. Lorry marvels at the horror of being buried alive for eighteen years.

Lorry’s dream foreshadows not only Dr. Manette’s return, but also the possible difficulties it will cause.

Lorry is feeling a little uneasy about recalling Dr. Manette to life.  He falls asleep and has a dream that seems to confirm that uneasiness.  In the dream, the metaphors turn into reality.  Dr. Manette is a ghost that Lorry has brought back to life, and he does not understand why he has been recalled.

“I hope you care to live?”
“I can’t say.”
“Shall I show her to you? Will you come and see her?” (Book 1, Ch 3, p. 11)

Dr. Manette tells Lorry that he has abandoned all hope of being dug out.  When Lorry digs him out, he is not quite sure what is going on.  Does he want to live?  He does not know.  It demonstrates Lorry’s uneasiness about bringing Manette back from the dead.  He is not sure Manette is ready.

Got out at last, with earth hanging about his face and hair, he would suddenly fall away to dust. (p. 11)

These events foreshadow the trouble Dr. Manette has with being freed from jail.  Although on the surface leaving jail is a wonderful thing, his mind has been someone shattered.  The jail and its death-like existence is all he knows.  Being taken out of that comfort zone is frightening to Dr. Manette, and Jarvis Lorry knows it.  He is worried that Manette will never fully recover.  When he asks Dr. Manette if he will come and see Lucie in the dream, the answers are “various and contradictory” with Manette sometimes crying and asking to see her and sometimes saying it will kill him if he sees her too soon.

Dr. Manette is imprisoned through no fault of his own.  Yet he has been there for eighteen years.  As they discuss in the dream, this is a long time.  He does not know Lucie.  He is both ready to see her and terrified.  He struggles with the relapses of his mind several times, whenever he comes across a situation he cannot face.

With these events, Dickens prepares us for a world that is not black and white.  Even supposedly welcome events have consequences, and things are not going to be easy for these people.

After receiving the message and responding to it by saying "Recalled to Life," Jarvis Lorry continues his ride on the coach to Dover, England on the coastline of the English Channel.  As he dozes on this coach with the night shadows hiding the faces of the occupants, "A hundred times the...passenger inquired of this spectre:  'Buried how long?'"

In Chapter III of Book the First, Mr. Lorry ponders what this resurrection of Dr. Manette will be like for the man who has figuratively buried for eighteen years as he was incarcerated in the Bastille.  In wonderment, Mr. Lorry exclaims,

"Gracious Creator of Day!  To be buried alive for eighteen years!"

 This resurrection of a man from his burial in prison, a symbol of the grave for Dickens, is the introduction of the important theme of Death and Resurrection in A Tale of Two Cities.  Along with Mr. Lorry, Lucie Manette effects the return to life for her father as he recognizes her golden hair and recalls his former existence as a physician and husband and father. Tragically, however, as a man brought back to life, Dr. Manette cannot shake off the effect that his incarceration, burial, and his being brought back to society have had on his mind.  Several times he regresses to his prison occupation of making shoes; however, with the love of his daughter and his own forgiveness for Darney, ne Evremonde, he is able to survive.

And, as a novel of dualities, this theme of resurrection is treated rather humorously with respect to Jerry Cruncher.  Digging up cadavers for physicians, Jerry euphemistically calls himself "a resurrection man."  Instead of mourners who were present for the funeral of these cadavers, Mrs. Cruncher instead "flops' onto the floor in prayer, begging the Lord to forgive her husband's sins.  Jerry, of course, returns no love to his wife; instead he accuses her of being an "Aggrawayter."  Ironically, however, it is Jerry's illegal occupation which leads him to the discovery that John Basard and Roger Cly and Solomon Pross are all the same man.

The dream and visions of Mr. Lorry in Chapter 3 of Great Expectations are very significant to the developing motif of duality.  In the previous  chapter, entitled "Night Shadows," Dickens rhetorically reflects that "every creature is constituted to be that profound secret and mystery to every other." In every room of every house there is a secret enclosed.  Now, in the latter part of this chapter, both the spiked hair messenger, Jerry Cruncher," and Mr. Lorry wonder who is "recalled to life."

In addition to the motif of duality, the theme of Redemption is introduced, a theme most significant.  Jerry, the reader later learns, calls himself a "resurrection man," and the man who has been buried eighteen years is also redeemed physically and spiritually.

You only get one question, I'm afraid; so I'll answer the first, which I presume is the most important. In A Tale of Two Cities, chapter 3, Jarvis Lorry is all bundled up in a coach with several other riders.  As he being jounced along the road, he has a dream.  First, he's in the familiar Tellson's Bank--the place in which he has invested his entire life.  Then his dream gets a bit odd.

A rather eerie figure appears in the dream, something Lorry calls "a spectre."  a similar event will happen three times in the dream, with just a slight variation.  Lorry begins to dig the man out, asking how long he's been alive.  The answer is "almost 18 years," and the spectre is asked if he cares to be "recalled to life."  The answers are yes, maybe, and no, a different answer in each dream scenario.  Jarvis also asks the spectre three times if he want to see "her."

“Shall I show her to you? Will you come and see her?”

The answer to this varies each time, ranging from a strong yes to a definite no. 

These images will soon be revealed as real people and real events in the novel.