I've had some pretty severe health problems throughout my life, and I had to spend a lot of time lying in bed/on the couch all day long, especially during High School. Movies that were moving, that had beautiful representations of the outdoors (I love being outside) and had great music helped to get me through.
Spirit was one of my all-time favorite "sick" movies. The fact that there is very little dialogue made it even better...there wasn't anything unnecessary for my sick brain to process. Just lovely animation and beautiful music. It made me feel free when I couldn't get outside. It will always be one of the most important movies in the world to me.