A Dream by Noon.

It is October 1994 in New England, and Samantha Mourey is a mess.
Once a little girl who was a nature loving free spirit. Little by little, the world, and probably genetics, bit away at that. Her empathetic and sensitive personality has led her to become a teenager who is anxious, depressed and doesn't know how to navigate this life that feels both foreign and also something that everyone else seems to have no problem with. She feels like a true outsider most of the time, with moments of happiness in between, until she meets Ryan.

After experiencing a traumatic panic attack at school, she ventures into an abandoned hospital to explore, and winds up in another place entirely. With the entire town looking for her, and other tragedies unfolding in the midst of it all, Sam has to make a choice if she wants to live in the real world or not in this Wizard of Oz meets Girl Interrupted sci-fi mystery.