 The second part is a randomized, double-blind, placebo-controlled study with a total of 72 participants divided into a intervention group 36 and a placebo group 36. In this part the investigators intend to investigate the analgesic, anxiolytic and sleep-promoting effects of melatonin. Melatonin and placebo will be administrated at 9 pm. the evening before surgery, 60 min. before surgery, immediately after surgery in the PACU and at 9 pm. the evening after surgery. 