After Macbeth kills Duncan, he thinks he hears someone say, “Sleep no more! / Macbeth does murder sleep.” He goes on to describe sleep in more detail:
… 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--
Macbeth has just stabbed his king, friend, and guest. He describes sleep as a beautiful repose for the troubled, temporarily relieving one’s physical and mental anguish. Murdering sleep involves destroying that peace. Macbeth fears that this act will cause him a permanent restlessness and anxiety. Not only is he tormented by his crime, both he and Lady Macbeth have difficulty sleeping. Lady Macbeth walks and confesses in her sleep, and Macbeth envies the resting dead. Duncan’s murder also interrupts the kingdom’s recently regained serenity. Once again, Scotland is plunged into chaos and violence.
Macbeth murdered Duncan in his sleep, and death, which is comparable to sleep, becomes more palatable to the agitated Macbeth than the life that he has created for himself. He lives in paranoia, guilt, and blood until his death.