You spend the night in a hospital bed after going to the emergency room with chest pain. Nurses check on you, doctors order tests and breakfast arrives on a tray. Naturally, you assume you’ve been admitted. Then a staff member hands you a form called the MOON and asks for your signature. What does it mean? That document is the Medicare Outpatient Observation Notice. It tells you that, despite spending time in the hospital, you are being treated as an outpatient. Under federal rules, the hospital generally must provide this written notice within 36 hours if your observation services last more than 24 hours. It must explain the notice aloud too.