Unless you're talking about some magical transformation, or some sort of advanced ability to change shapes along with the user's experience of new shapes, I guess if you drastically changed your body, it would take a great amount of time getting used to it. Consider something as extreme as being changed from a human to a pony;
1) You would have to change your skeletal structure, as well as add / remove certain parts of it.
2) Your center of mass would be entirely different, and you would need to adjust your movement appropriately. Even something which you have come to embrace as natural - such as moving - would feel weird and you will probably go through vertigo trying to move around in your new body.
3) On a side note, all of your instincts and muscle memory are human-centric. That means that you will have to learn using body language and natural reactions to different scenarios all over again.