What does it mean that Macbeth killed the sleep itself in Macbeth?

Macbeth murdered Duncan and the guards as they slept, and now he feels bad about it.

Macbeth is already a bit delusional at this point.  He was nervous about committing the murders, and once he did so he felt guilty.  Macbeth is having delusions because he feels as if the people he murdered are haunting him.

Macbeth thought he heard the men he murdered praying, and he was unable to pray in return.  This makes...

Macbeth murdered Duncan and the guards as they slept, and now he feels bad about it.

Macbeth is already a bit delusional at this point.  He was nervous about committing the murders, and once he did so he felt guilty.  Macbeth is having delusions because he feels as if the people he murdered are haunting him.

Macbeth thought he heard the men he murdered praying, and he was unable to pray in return.  This makes him think he is damned or cursed.  He also imagined one of the men accusing him.

Methought I heard a voice cry 'Sleep no more!
Macbeth does murder sleep', the innocent sleep,
Sleep that knits up the ravell'd sleeve of care,
The death of each day's life, sore labour's bath,
Balm of hurt minds, great nature's second course,
Chief nourisher in life's feast,-- (Act 2, Scene 2)

Macbeth will not be sleeping peacefully any time soon.

This is the first time that Macbeth begins to show signs of remorse and paranoia.  His wife tries to comfort him and tell him that it’s nothing, but he is all out of sorts.  She talked him into it, he did it, and now he is really horrified.

Macbeth’s slide into insanity is quick from here.  With each murder he commits he gets worse.  After killing Banquo, Macbeth is convinced that he sees Banquo’s ghost at dinner.  He also wants the witches to tell him what is going to happen and reassure him.  He finds their new prophecies less than satisfying though, because they are contradictory and incomplete.

Macbeth fears that he will be found out.  This is why he kills Banquo, and tries to kill Macduff.  However, his irrational behavior and his killing spree also lead to his wife’s death.  Macbeth is a harbinger of destruction.  He finds that he has to keep going until he destroys himself, or is destroyed.