This literature review explores neurocognitive function in hyperbaric environments by outlining the pathophysiological processes that underlie experiences of narcosis in freedivers and emphasizes the utility of critical flicker fusion frequency (CFFF) in targeted studies. Nitrogen narcosis, or inert gas narcosis (IGN), is a well-described phenomenon with potentially fatal consequences. On descent, cognitive alterations and psychomotor manifestations are primarily linked to scuba diving. However, symptoms are reported by apnea divers too and typically culminate on ascent. Elite freedivers regularly exceed depths where narcotic effects are suspected to set in, yet underlying mechanisms remain incompletely understood. Neurological impairments may originate from dissolved breathing gases that interact with nervous tissue or from hemodynamic responses tied to the apnea diving profile. Specific sites of action are neuronal membranes, neurotransmitter substrates, and the blood-brain barrier (BBB). Considering its correlations, confounders, and deployment in hyperbaric conditions, CFFF thresholds could reflect the respective changes in brain performance, both onshore and underwater. Related experimental designs involving freediving professionals might delineate the onset and progression of symptoms at various diving stages. Thus, providing possibly valuable insights into the pathophysiology of narcosis by comparing baseline values to relative measurements taken at depth and upon resurfacing. Research on sites of action, individual susceptibility, and CFFF associations, along with neurovascular coupling and the effects of hyperbaric gases on neuronal modulation, is crucial. Eventually, studies using CFFF as a proxy for neurocognitive function may optimize health and performance outcomes in freediving scenarios.