what is one major difference in the style shakespeare uses for act 5 scene1 versus the others? why does he do this?
One major difference in style between Macbeth V.i and the rest of the play is that the scene takes place in darkness, lit only by the candle Lady Macbeth brings on stage as she sleepwalks. Her lady in waiting comments that Lady Macbeth "has light by her continually; 'tis her command."
Fearing the dark, Lady Macbeth insists on the light of a candle to ward off her fears, anxiety and guilt. Yet, even as she sleeps, her troubled conscience drives her to walk, talk, and relive her evil deeds. In her sleep, Lady Macbeth washes her hands compulsively in an effort to cleanse her guilt. She proclaims that she and Macbeth have no need to fear punishment for their evil deeds when she says, "What need we fear who knows it, when none can call our power to account?" Yet she also expresses her fear of eternal damnation: "Hell is murky!"
Of course, when Shakespeare wrote this play, theater took place in daylight under an open sky. After all, there were no electric lights. During this time, playwrights used props like lit torches or candles to indicate darkness and audiences used their imaginations to complete the scene. Shakespeare set this scene at night because the darkness represents the condition of Lady Macbeth's troubled heart and conscience.
Another major difference is that almost all of V.i is written in prose.
Shakespeare uses blank verse--unrhymed lines of iambic pentameter--most of the time. Blank verse has ten syllables per line with every other syllable accented (emphasized), starting with an unaccented syllable.
However, when a common or lower class character speaks, Shakespeare generally writes their lines in prose. Prose is the kind of language we speak, read and write every day. Prose is written without concern for the way the words sound (meter or rhythmic patterns of the words, rhyme, alliteration, etc.). Lines of prose end when the text reaches the right margin; lines of verse end when the author chooses.
Sometimes Shakespeare uses prose to indicate that a character is vulgar or morally diminished. In Romeo and Juliet, Juliet's nurse speaks in prose because she is a peasant--a commoner. Mercutio, on the other hand, is a nobleman--he is, in fact, related to the prince. Yet he speaks in prose, too. Why? Mercutio's prose reflects that fact that his character is somewhat crude and base. He makes vulgar sexual innuendos and implies that Romeo's feelings for Rosaline are nothing more than sexual impulses (which, of course, they likely are).
Given the way Shakespeare uses verse and prose, it makes sense to conclude that the lady in waiting and the doctor use prose in Macbeth V.i because they are not nobles. Lady Macbeth, on the other hand, uses prose because, while she is a noblewoman, her moral state is very base.