The lore text about vampires (MM, p. 295) states (emphasis mine):
Every vampire remains bound to its coffin, crypt, or grave site, where it must rest by day.
How should this be interpreted? Does it simply mean that vampires can only sleep in their coffin (or similar), and if they don't, they just suffer the usual exhaustion rules for not sleeping?
Or are there other consequences? There doesn't seem to be additional information in the 5e Monster Manual, so information from previous versions or general vampire lore is also valid.
(I'm not considering differences between PC and NPCs/monsters. Sure, NPCs usually don't take rests, but that's just for convenience reasons. If the vampire is your BBEG, he might run away and heal up with a short rest before the players catch up to him. So my question disregards whether the vampire is a PC or NPC.)
As a side note, do vampires actually sleep at all? The general undead theme seems to be "no food, drink or sleep", so do vampires "resting" in their coffin simply linger around awake for 8 hours to get a long-rest's benefits?