Although the function of sleep is not fully understood, it is generally accepted that it serves to recover from previous wakefulness and/or prepare for functioning in the subsequent wake period. An individual’s recent sleep history therefore has a marked impact on their daytime functioning. Restricting sleep to less than 6 h per night for four or more consecutive nights has been shown to impair cognitive performance and mood (Belenky et al., 2003), disturb glucose metabolism (Spiegel et al., 1999), appetite regulation (Spiegel et al., 2004) and immune function (Krueger et al., 2011).