Sleep is a key medium through which foreshadowing occurs in Dracula. Any character who has bad dreams or trouble sleeping is marked for future affliction, as Lucy is in Chapter 6:
Lucy has not walked much in her sleep the last week, but there is an odd concentration about her which I do not understand; even in her sleep she seems to be watching me. She tries the door, and finding it locked, goes about the room searching for the key.
Lucy's trouble sleeping foreshadows Dracula's interference and attack, as well as Lucy's future death and mutation into a vampire. As Lucy's sleeping troubles worsen, so does her death harken nearer, as Dracula preys on her at night. This reappears as a motif in Dracula, with both Mina and Jonathan having bad dreams and/or trouble sleeping as a prelude to danger.
As a means of foreshadowing tragedy, sleep is a particularly terrifying medium. Human beings are in their weakest, most vulnerable state while sleeping, readily available for exploitation. As a means of generating tension and contributing to the general mood of foreboding and horror, Stoker could not have made a better creative choice. In removing sleep and nighttime as sources of respite, Stoker ensures that both his characters and his readers remain on edge.
