Look.. train does not start at once. so if you are facing the engine side then you will not feel any sudden jerk. But train may apply brakes suddenly, so it may give a sudden jerk while stopping. So, if you face engine side, then on stopping you wil fall forward, and if hte jerk is strong then there are chances that you may even fall from your seat. but if you face guard side, then on sudden stopping you will just get pushed into the cushion at your back and will not fall below.
I hope you people don't get frustrated with all this kind of non-sense post, but it helps many times. :)