Those qualifying will receive suvorexant 20 mg and placebo for each of 9 nights in a cross over design with 7 nights of washout between treatments. Overnight sleep recordings (PSGs) will be collected on nights 7 and 8 of each crossover treatment arm to determine objective sleep measures. During the day following night 7 in each arm, a Multiple Sleep Latency Test (MSLT) at 1000, 1200, 1400, and 1600 hr will be conducted and nociceptive sensitivity [finger withdrawal latency (FWL)] testing to a radiant heat stimulus (1100 and 1500 hr) will be conducted on day 1 and day 8. Self-reported mood and pain indices will also be completed prior to each FWL test.