Some manage to stay Lucid during hours, yes.
What about those who did not?
They keep training
But what happen to these Undead practitioner when they are sleeping. That’s the part I don’t get.
They train staying Lucid in their dreams.
In many point, Death is comparable to a sleep. This is described in the Tibetan tradition as the state of Bardo, the world of illusion. By becoming Lucid, we understand that we are experiencing a (shared) illusion and become capable of taking control of it.
Can I use vampirism to weaken a target without doing harm so I can persuade them better with magick?
-Don’t had a banefull intention to your action.
-Don’t drain too much. Vital energy tend to renew itself (not all types, that being said) with rest and sleep. If you don’t do it on a regular base and don’t had any aggressive intention to your action, the energetic level of the subject will come to normal with one or two nights of good sleep.