A vampire can always sleep longer than 8 hours, but it is a minimum duration required. While in the grave or coffin, a vampire falls into such a deep sleep that they are powerless and can sense nothing. Likewise, nothing will awaken them, once they have succumbed to the sleep of the dead. Despite their various advantages, vampires have their weaknesses as well. Crosses and religious artifacts, with their purity, burn vampires and ward them away.
Vampires also suffer from holy water, treating it like acid.
Sunlight turns the vampire into ash, rather painfully. Garlic prevents a vampire from approaching, or attacking. They show no reflection in mirrors, and cannot cross large bodies of water. They cannot enter homes they have not been invited into. A wooden stake through their heart paralyzes them, while fire, decapitation, and other methods involving major destruction of the body will destroy them utterly.