Polysomnographic measurements have been of critical importance in evaluating the interaction between sleep and physiological changes (Murali et al., 2003). Thanks to polysomnographic measurements, the effects of sleep can be objectively differentiated from the effects of rest and recumbency. The specific effects of sleep onset, sleep termination, and the effects of different sleep stages, can be assessed (Haex, 2004). When measuring sleep, subjective measures or self-evaluations are often used and are valuable, however show a high level of vulnerability to external and motivational factors (Curcio et al., 2001).