Astral Perception, Enter the Realm of Dreams Options

[Stahlseele]

it's no question about the rules wise aspect, just somthing i thought up while at work and my brain decided to take a little time-out.
How is Astral perception/travel accomplished? either by sheer willpower and determination through a good bit of concentration or by meditating and relaxing?
If it's accomplished by relaxing . . what happens if the mages go to sleep? O.o there's not many states you can be in that are as relaxed as sleeping is i would think . . so would a mage suddenly go astral sleepwalking? would an adept not really dream because he's merely astrally percieving(Spelling check? that does not look right to me somehow) while his meat body is relaxing and resting?
If it's done by concentrating . . imagine you really concentrating on something really hard because you wanna accomplish something important to you . . or going to the loo . . do you suddenly shift on the astral plane? o.O