"Faithfully imagine the end and all things conspire to aid you in your harvesting." - Neville Goddard

In order to manifest my desires, one of the most effective methods I use is the visualization technique. I plan a scene where I am successful in my desire, 'the end'. 

Falling asleep while in the state only adds to the certainty of its manifestation. On most occasions I do not fall asleep while in the desired state. But doing it at night time before bed, your conscious is shutting down and therefore all of your imaginal acts are received directly without filter to your subconscious mind.

The point is that when one does fall asleep while imagining, you are visualizing a scene and that scene is continued while your conscious is completely shut off. When your conscious is completely shut off, the scenes which are presented to it are perfectly recreated by your subconscious mind.

With a more definite definition, the Subconscious mind recreates feeling. It doesn't see, but it feels the feelings of what you see. Whatever it feels, it recreates. The conscious is a filter which adds different feelings and emotions, or prevents images and feelings from entering the subconscious mind.

At night and early in the morning upon awakening or when retiring at night, the conscious is at its least active state -- therefore your subconscious is directly impressionable.

So when Neville explains that if you fall asleep in the state, then it is done, that is the IDEAL to work toward. One very important part that it seems you've missed is that Neville says he "gets into a state akin to sleep". That means that he gets past the part of the wandering thoughts and the "todo lists". After he has tamed his mind in that session to move past those distractions that you've programmed into your subconscious mind, THAT is the state akin to sleep.

Simply closing your eyes is not a state akin to sleep. But commanding your subconscious mind to relax and pay attention, and then receiving her cooperation then allows you to be in a state akin to sleep.

Anyway, the point is that the more susceptible your subconscious mind is to impression, the greater the results.

To conclude, I've been doing this a while. It's a 50/50 shot that I fall asleep while visualizing. When I do, it is 100% certainly done. When I do not fall asleep, I get almost the same results.