Looking for transformed and amnesiac characters in fantasy fiction

Der Trish, you and Alessan both hit on exactly the imagery I was looking for. Thanks.

Have you read Sylvester and the Magic Pebble by William Steig? It’s a Caldecott Medal winning children’s book whose plot sounds like what you’re talking about.

In A Wizard of Earthsea, Ged changes to the form of his namesake, a sparrowhawk, to escape a minor god and forgets how to change back. The change would have been permanent if his mentor hadn’t helped him find his true form again.

Morgan in The Riddlemaster of Hed is shipwrecked and loses both his memory and the ability to speak until a companion helps him recover.

Between Avram Davidson’s novels Peregrine: Primus and Peregrine: Secundus, the titular hero spends time transformed into his namesake, a peregrine falcon. He gets better.

I read that book years ago as a kid and I don’t know if that would qualify according to the OP. As I remember, Sylvester unfortunately retains his memory while he’s a rock and is fully aware of each and every stupefying boring moment of existence as an inanimate object.