Emergent research suggests that “fear of missing out” (FoMO)-driven nocturnal use of social media may result in sleep disturbances and adversely influence quality of sleep. Previous research in this area primarily focused on adolescents. Therefore, knowledge of these occurrences in young adults is limited. This study addresses this knowledge gap by investigating the associations of FoMO, psychological well-being (anxiety, depression), compulsive social media use (CSMU), and sleep hygiene (habits that promote/inhibit sleep) with problematic sleep adults in both academic and employment settings. Cross-sectional surveys were conducted to collect data from two cohorts including (i) full-time students (N = 1398), and (ii) full-time working professionals (N = 472). Data were analyzed with structural equation modeling. The results indicated that psychological well-being influences CSMU, which in concurrence with sleep habits, influences the association between FoMO and problematic sleep. Significant differences existed in the strength of the association between CSMU and FoMO between the two cohorts. Interestingly, FoMO is more strongly associated with CSMU among working professionals. This study provides novel insights into the differential effects of CSMU and FoMO on sleep behaviors in young adult students versus working professionals.