Abstract: An insomnia or vigilance monitor comprising one or more electrodes (1a,1b) for obtaining an electrical signal from a subject over a period of epochs, the electrical signal being related to the sleep or wakefulness stage type being experienced by the subject; and a processor (5) adapted to analyze the electrical signal and assign a sleep or wakefulness stage type to each epoch to generate a hypnogram. Methods of monitoring sleep or vigilance using the mastoid site are also disclosed. Further disclosures relate to a method of training and testing a first neural network for use in a physiological monitor, and a method of assigning a class to an epoch of a physiological signal obtained from a subject as a set of samples.