Falling into nothingness: Modeling suicidal ideation as the person × situation interaction of personality functioning and loneliness.

= 18.82, per participant). Impairments in personality functioning were associated with higher mean levels of loneliness and SI. At the same measurement point, within-person increases in loneliness were associated with heightened SI, particularly among individuals with more severe impairments in personality functioning. Prospective models failed to identify a significant lagged effect of loneliness or its interaction with personality functioning; only trait-level loneliness and the level of personality functioning remained predictive of subsequent SI. Findings support a Person × Situation interaction model of SI, indicating that experiences of loneliness are a particularly strong risk factor for SI for individuals with low levels of personality functioning. By integrating trait- and state-level perspectives on risk, ecological momentary assessment offers a promising tool for capturing dynamic processes and real-time, personalized intervention approaches. (PsycInfo Database Record (c) 2026 APA, all rights reserved).