Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for visualizing, scoring, recording, and analyzing sleep data and hypnograms. In some implementations, a method includes generating and providing a representation of sleep stages that includes a sequence of elements indicating a progression of the sleep stages over time during a sleep session. In some implementations, a method includes generating and providing one or more scores based on analysis of the sleep session. In some implementations, a wearable body data recorder includes a plurality of sensors and is configured to measure and process sensor data obtained during a sleep session of a subject.