HCRT and hypocretin deficiency: Only in mini-epochs, sleep-wake fragmentation was (a) higher in patients with severe core symptoms, and (b) increased in the 2nd night-half in NT1 patients with severe hypocretin-1 deficiency (<40 pg/mL) and/or severe core symptoms.<h4>Conclusions</h4>Our findings suggest that sleep fragmentation, a core feature of NT1, is associated with disease severity and hypocretin deficiency severity when high-resolution sleep stages are analyzed.