Salivary levels of Melatonin and Cortisol: Saliva will be collected by placing wool swab of plain Salivettes (Sarstedt, Disposable Products, Regency Park, Adelaide) into the mouths of the subjects with chewing for 5 min. Saliva samples will be taken at a total of 18 time points over a 36-h period for each subject. The samples will be kept in Salivette tubes in the refrigerator at ±4 ºC until the end of each 24-h period. The Salivette tubes will be centrifuged for 15 min at 3000 ´g and the samples frozen at -20 ºC until assayed.