In European folklore, vampires were often reported as sleeping in their coffins, with blood around their mouth and the left eye open. The vampire would often be wrapped in its funeral shroud, and its teeth, hair and nails may have grown, though the body is dead. Corpses suspected of being vampires were described as bloated and purplish in hue (appearing to be full of blood), with little or no decomposition and a healthier appearance in general than would be expected. The belief therefore arose that vampires hunted their prey at night and returned to their coffins to sleep during the day.
In reality, these fears may have arisen from a lack of understanding of the decomposition process. Decomposition can vary depending on temperature and soil composition, with some bodies appearing to decay quicker than others. Gases in the corpse cause the body to swell, and the increased pressure forces blood out from the nose and mouth, as well as giving the body a bloated and ruddy appearance.
Dracula himself does not return to his grave at daybreak, but seems instead to sleep in a substitute coffin; a long wooden box. Dracula’s sleeping habits may reflect an undead creature’s preference for a bed better suited to the dead. In some forms of the vampire myth these unholy creatures are burned or repelled by the light of day, which is why they need to seal themselves in coffins during daylight hours. This does not seem to be the case with Dracula, who is only weakened during the day. Dracula also sleeps in newly dug earth; as Van Helsing later explains, this is because vampires need to sleep on the soil of the consecrated ground (graveyard) in which they were buried. This seems odd, as other holy things repulse vampires, but perhaps the earth has been corrupted by the vampire's presence.
The use of coffins, connection to graveyard soil, and hatred of daylight are all vampire features that vary considerably in fiction. At extreme ends of the scale in recent fiction are the vampires of True Blood, who ignite in the sun and must sleep in dark, sealed places, and the vampires of Twilight, who simply avoid direct sunlight (it gives away their true nature) and never sleep.