Flyer by Ciaran Connelly
Challenger Deep was written by Neil Schusterman. It is about the mental and physical struggles of two characters, who might be the same people.
The main characters of the story are Caden Bosch, a high school student with serious anxiety, and Caden Bosch, a crew member of a strange ship searching for treasure. A few other characters are the parents of high school Caden, and the Captain and a parrot on the ship.
When the book starts out, high school Caden is starting to experience more and more anxiety, while ship Caden is on some mysterious ship that is very vaguely described. In the climax of the book, high school Caden is put in a mental hospital, and ship Caden has to dive into the waters of Challenger Deep, causing him to meet a sea serpent. In the end, it becomes clear that both Cadens are the same, and Caden becomes free from his anxiety, at least for a while.