Sora has had a bad three months. Get a Nightmare, get a Keyblade, watch your home be destroyed. Almost die every hour of the rest of your life. Get almost killed by your best friend. Learn Magic. Kill people. Kill Monsters from your nightmares. Kill corpses. Fight a guy with the power of GOD! Sora is just tired now.
So when he wakes up a Pony, and everyone is super friendly, and magic is really common? Screw it, he's going to take this break, even if he has died like... Four times now.