Circadian fatigue, largely caused by sleep deprivation, significantly diminishes alertness and situational awareness. This issue becomes critical in environments where auditory awareness - such as responding to verbal instructions or localizing alarms - is essential for performance and safety. While head-mounted displays have demonstrated potential in enhancing situational awareness through visual cues, their effectiveness in supporting sound localization under the influence of circadian fatigue remains under-explored. This study addresses this knowledge gap through a longitudinal study (N=19) conducted over 2-4 months, tracking participants' fatigue levels through daily assessments. Participants were called in to perform non-line-of-sight sound source identification and localization tasks in a virtual environment under high- and low-fatigue conditions, both with and without head-up display assistance. The results show task-dependent effects of circadian fatigue. Unexpectedly, reaction times were shorter across all tasks under high-fatigue conditions. Yet, in sound localization, where precision is key, the HUD offered the greatest performance enhancement by reducing pointing error. The results suggest the auditory channel is a robust means of enhancing situational awareness and providing support for incorporating spatial audio cues and HUD as standard features in augmented reality platforms for fatigue-prone scenarios
