Clinical diagnosis of sleep disorders, which are recognized contributors to morbidity and mortality, often relies on polysomnography (PSG) data. However, the vast physiologic data collected during PSG is underutilized, presenting a key opportunity to enhance characterization of sleep dysfunction and predict clinical outcomes. We introduce a sleep foundation model that uniquely integrates PSG time-series signals and electronic medical record data. Using a diverse dataset (n=10,000; mean observation period 14.5±7.1 years), our transformer-based model generates data-driven representations of latent physiological patterns. When clustered, we identified subpopulations with differential health trajectories. The highest risk-group exhibited strong correlations with all-cause mortality (unadjusted hazard ratio [HR] 4.83, 95% confidence interval [CI] 3.60-6.50, p<0.001) as well as cardiovascular outcomes and neurological outcomes, even after accounting for traditional measures. External validation in a National Sleep Research Resource cohort confirmed findings. We created a novel, clinically applicable framework leveraging information-dense PSG data to inform risk stratification and predict health outcomes beyond traditional methods.