Is six hours of sleep at night enough?
Seven would be better at your age. Six is the minimum, at any time except in old age.
The ordinary period of sleep most people give themselves is 8 hours. In bad health (I am not speaking of acute illness) it can extend to 9. 12 hours is excessive unless one is seriously ill or recovering from illness or else has underslept for a long time and the body is making up arrears of needed sleep.
There is no reason at all why intensity of sadhana should bring insufficient sleep.
What is the cause of the “wrong kind of sleep” you spoke of?
The “wrong” kind is usually a heavy subconscient sleep — when inertia prevails, one is likely to get that kind of sleep.
Sometimes in my dreams, there is an accident or a dangerous happening. Its shock is felt even when I wake up.
It comes sometimes in dreams — there is an effect of some inner shock or alarm on the body consciousness, which lasts after the dream state is over.
At noon there is an urge to sleep. During the sleep I pass through ordinary or sometimes even lower dreams. And yet when I wake up I feel quite concentrated and withdrawn in peace. Today there was an utter silence for a long time.
One passes through several states in sleep or even some part of the being may be in the lower dreams, another in silence during the sleep.
I tried in the morning to concentrate on the sadhana but did not completely succeed. Yet when I got up from my noon nap, I found a great and spontaneous flow of force, which lasted through the whole evening. How could sleep bring about such an effortless state?
I suppose in sleep the mind and vital don’t interfere — so the force called by the effort of concentration has its chance.
It is usually only if there is much activity of sadhana in the day that it extends also into the sleep state.
In dreams and visions how can we be sure that what we see or hear is from you or Mother and not from an anti-divine force taking your form or imitating your voice?
You cannot be sure unless you have sufficient experience and consciousness to discriminate. There are several people who have constructed an image of the Mother or myself and they come and say the things the person would like or expect them to say.
 “They” refers to the images of Mother and Sri Aurobindo.