1. A method comprising: identifying sleep states of a subject during a period of time based on polysomnography; recording values of a non-polysomnographic physiological parameter set of the subject during the period of time; subsequent to identifying the sleep states and recording the values of the non-polysomnographic physiological parameter set, correlating the recorded values of the non-polysomnographic physiological parameter set to the identified sleep states using a computing device; subsequent to correlating the recorded values to the identified sleep states, analyzing the correlated values of the non-polysomnographic physiological parameter set using the computing device; subsequent to analyzing the correlated values, calculating a relationship between values of the non-polysomnographic physiological parameter set and sleep states based on the analysis using the computing device; and subsequent to calculating the relationship, storing the relationship between values of the non-polysomnographic physiological parameter set and sleep states in a medical device, wherein the medical device is configured to apply the relationship to a non-polysomnographic physiological parameter to identify sleep states based on the relationship.