A Study of the Effect of Daridorexant on Nighttime Body Posture, the Noise Level Required to Wake up, and the Ability to Remember Words Previously Presented

Inclusion Criteria: * Signed informed consent in a language understandable to the subject prior to any study-mandated procedure. * Male and female subjects aged 18 years or older at Screening (18 subjects must be 65 years or older). * Woman of childbearing potential (WoCBP) who has a negative serum pregnancy test at Screening and a negative urine pregnancy test on Day 1 pre-dose. She must agree to use consistently and correctly (from Screening, during the entire study, and for at least 5-7 days after last study treatment administration) an acceptable method of contraception with a failure rate of less than 1% per year, be sexually inactive, or have a vasectomized partner. If a hormonal contraceptive is used, it must be initiated 1 month before first treatment administration. * Woman of non-childbearing potential, i.e., postmenopausal (defined as 12 consecutive months with no menses without an alternative medical cause, confirmed by a follicle-stimulating hormone \[FSH\] test), with previous bilateral salpingectomy, bilateral-oophorectomy or hysterectomy, or with premature ovarian failure (confirmed by a specialist), XY genotype, Turner syndrome, or uterine agenesis. * Body mass index (BMI) of 18.0 to 35.0 kg/m2 (inclusive) at Screening. * Ability to communicate well with the investigator, in a language understandable to the subject, and to understand and comply with the study requirements. Exclusion Criteria: * Known hypersensitivity to daridorexant, or treatments of the same class, or any of its excipients. * Any known factor or disease (e.g., unstable medical condition, significant medical disorder, or acute illness) that might interfere with subject's safety, study conduct, or interpretation of the results, such as * History of narcolepsy. * Shift work within 2 weeks prior to Screening, or planned shift work during the study. * Travel across 3 or more time zones within 1 week prior to Screening, or planned travel across 3 or more time zones during the study. * Previous (i.e., within 2 weeks prior to first study treatment administration) and ongoing treatment with any prescribed central nervous system (CNS)-active medications, and/or diuretics that would affect nighttime rest, and/or moderate to strong cytochromes P450(CYP)3A4 inhibitors or inducers.