It depends. Pay them a visit. Tell them you have a significant mental illness but you are stable. You'd like to know what they might need to allow adaptations should you start having symptoms. They may need an MD's letter. They may take your word for it. Different schools do different things. The university my daughter works at only requires back-up documentation when the adaptation is significant (like a long absence for a hospitalization) or requires expensive adaptive equipment like a braille note or screen reading technology.