The answer is about force.
If the train is travelling at a constant velocity (in all 3 spatial dimensions), then regardless of how long you are magically suspended in mid air , then when you land it will be in the same place. This is because there is no net force being applied to you, or the train. (The force the train is exerting is being used to overcome resistance to motion, and st a constant velocity they exactly cancel each other out).
If, however, the train is accelerating or decelerating - again in any of the three spatial dimensions - then you would move during your magical suspension. Probably the best example is if you went around a corner: the train is being ‘accelerated’ to one side, but you would not be. You would then end up, fairly gently, in contact with the inside side of the train, at which point you would then start to experience the same acceleration as the train. You will experience this acceleration every time you go round a corner on a train, particularly if you are standing up and not holding on to a grab pole.
As others have said, the accelerations a train is capable of under normal circumstances are rather gentle, and the air in the coach also imparts a certain amount of resistance. Emergency braking (nominally 12%g) means that if you were travelling in a coach that was a perfect vacuum, and had a ‘hang time’ of 1 second, you would only move forward 0.6metres relative to the coach.