Abstract: Insomnia is a prevalent sleep disturbance in the general population. As standard diagnostic method for assessing the nature and the severity of the sleep problem, a so-called sleep log or sleep diary, i.e. a questionnaire usually on paper, is used in most cases. The main drawback of this diagnostic tool is that its accuracy is affected by subjective bias of the patient, e.g. for patients it is often difficult to remember sleep and wake periods during the night correctly. The present invention proposes an automatic sleep log that uses vital body signs as input signals for assessing sleep and wake periods during the night. By using objective data, the diagnosis will be more accurate. Furthermore, this system can also be used to sleep restriction therapy, a non-pharmacological method to treat insomnia. Also in this application it can contribute to patients correctly applying this method and thus leading to a better medical outcome.