Right it's all to do with the fact that your centre of gravity is somewhere near your solar plexus, that is to say the top half of your body weighs more than the bottom half.
You will notice when they perform this stunt that they do so in front of a crowd, and in doing so they've already built up a sense of expectation. By positioning two people to your rear to catch you, this sense of what your expected to do is reinforced subliminaly. Not dis-similarly, the chances are you've already watched a few stooges perform the 'falling backwards' routine, so the sense of conditioning is complete.
The next thing to do of course is ensure you fall over. Notice that you're always told to stand with your feet close together. Well next to each other in actual fact. The objective is to try and present the smallest possible base. You're never asked to stand with your feet 3 foot apart with one foot forward and the other backward, like you might if you were tight rope walking for instance. Your toes will provide some counter balance towards a forward movement but there is nothing to check a backwards movement.
The next thing they do is get you to stand with your arms in tight by your side. Clearly extending your arms out at 90 degrees aids balance, and this isn't in their interests.
What you've done therefore is present a top heavy object, on a small base. However, to ensure that you'll lose balance it becomes necessary to deny the brain a horizon line to focus on, which is why you are made to close your eyes.
Now of course you're told to relax and allow God to enter you etc and when this starts to happen just surrender to it etc
If you do this at home, after about 30 seconds of relaxing in this manner you should start to experience a slight loss of balance. You will be able to correct this if you choose to, but if you've been conditioned into thinking that its God entering your soul and that you're to allow it to happen, you will eventually start to fall backwards. This doesn't manifest itself as a dramatic collapse, but just a gentle sway, if you've been prepared however to believe this is God, then you're more likely to allow the momentum to take you over.
I would imagine about 80% of you should be able to achieve this without a crowd whooping it up or me encouraging you with soft relaxing whispers of how God loves you and what's you to join him etc
Happy conversion folks and come and join Warblers Church of seventh day wacko's and assorted spacemen.
Next lesson - God will demonstrate he exists by sending me a sign. That is to say he will buy me a 6 bedroomed house, with swimming pool and Rolls Royce, but first he will require you to give me some money so he can be convinced your worthy of his attention.