Mind After Midnight

This study examines whether wakefulness during the biological night (2:00-4:00 AM) is associated with increased negative mood, impaired decision-making, and suicidal thoughts. Adults with a history of suicidal ideation in the past six months will complete laboratory and home-based assessments under varying levels of sleep pressure. Participants will be evaluated during late-night wakefulness and under conditions of both higher and lower sleep pressure. The goal of the study is to better understand the biological and behavioral mechanisms that may contribute to elevated suicide risk during nocturnal wakefulness.

Inclusion Criteria * Age 18-55 years * History of suicidal ideation within the past 6 months * Habitual bedtime between 9:00 PM and 1:00 AM * Habitual wake time between 6:00 AM and 9:00 AM * Ability to provide informed consent Exclusion Criteria: * Current suicidal intent requiring immediate clinical intervention * Diagnosis of a primary sleep disorder (e.g., untreated obstructive sleep apnea, narcolepsy) * Bipolar disorder or psychotic disorder * Substance use disorder within the past 3 months * Use of medications that significantly affect sleep or circadian rhythms * Night shift work or transmeridian travel within the past month * Medical or neurological condition that would interfere with participation * Pregnancy