Emerging adults (ages 18-29 years) in post-secondary school experience significant disruptions in sleep and increased vulnerability to mental health challenges. One burgeoning mental health concern that may be exacerbated by poor sleep is nonsuicidal self-injury (NSSI). Prior cross-sectional studies have shown that poor sleep is commonly reported among young adults who engage in NSSI. However, daily diary studies examining within-person variability in nightly sleep (and deviations from one's typical sleep patterns) in relation to NSSI urges and behaviors are scant. It is also unclear which individuals may be most vulnerable to the effects of poor sleep in daily life. The associations among sleep duration, sleep quality, NSSI urges and behaviors, and two potentially relevant moderators (i.e., self-criticism and pain tolerance) were examined in the present study. Participants (N = 160, 83% female, M_age = 19.75, SD = 1.8) completed 14 days of daily entries (88.6% completion rate), resulting in 1982 assessments. Hierarchical linear modeling revealed that sleep duration the prior night, but not sleep quality, predicted NSSI urges and engagement among those with high self-criticism. These findings underscore the role of sleep duration and self-criticism in NSSI and suggest that young adults with heightened self-criticism may be particularly vulnerable to NSSI in the context of inadequate sleep.

Keywords: Daily life; Nonsuicidal self-injury; Post-secondary students; Self-criticism; Sleep duration; Sleep quality.

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