Well, depends on what you believe, in some cultures, religions and paths. People think that you can become a non-human creature when you die or transcend to another metaphysical plane, just like a demon, an angel or a youkai. Other thinks that it is possible that your spirit couldn?t be from a human but from another creature that could be an animal or a mythical one such as a vampire or an elf. But what we know is that you can?t be one of these mentioned creatures, as they defy the laws of nature that were given to us.
Imagine a human of 5?9? in length, which could just transform into a bear that doubles their length and weight. It wouldn?t make sense because it would need a total change in your structural DNA, your bones becoming larger along your mass at a fast pace than a human could grow in a year, growing hair/fur also at a very accelerated pace, it would just wear down the human hair follicles very fast, and finally brain wiring your brain from the human dialect to the bear?s along your vocal chords, then they could change back to their human state without any problem, mentally or physically. It doesn?t really has sense for me if you ask.