Sleep as a repair operator, not a symptom: linking energetic triage to overnight restoration in depression

Energetic triage models describe depressive symptoms as the output of a regulator that, under energy shortage, restricts costly and deferrable functions. Separate literatures show that sleep restores brain energy reserves and synaptic balance. In a non-systematic review of frameworks linking depression to energetics, we show that sleep appears in them as a risk factor or symptom, or not at all, never as the process that closes the daily energetic loop. We propose that sleep is a repair operator that reverses the daily drift in synaptic state and energy reserves. Higher functions can lack energy at constant consumption, because the cost of tissue maintenance rises during wakefulness (overhead deficit). The regulator responds to deficit accumulated from many sources, which periods of surplus repay with triage-dependent efficacy (signed deficit integral). Chronically incomplete overnight restoration is one route of accumulation, overlooked in triage models; whether the day is closed depends on sleep quality, not only on its amount. Beyond a threshold, triage also cuts repair and investments that rebuild capacity, which explains persistence, slow recovery and faster relapse. In the subtype defined by energy-related symptoms (fatigue, prolonged sleep, increased appetite), we predict smaller overnight restoration at equal sleep amount and structure, measured by gray-matter phosphocreatine and EEG markers of wakefulness. Course should be predicted by overnight restoration, not by fatigue. We state conditions that would falsify the core, registered before data, and measurement requirements: sleep quality measured separately from duration, and flow and deficit balance instead of levels. The mechanism remains untested. Preregistrations (OSF): Core predictions P1–P7 and falsification conditions F1–F6 (2026-10-29): https://doi.org/10.17605/OSF.IO/UERFG Predictions concerning interventions (2026-10-05): https://doi.org/10.17605/OSF.IO/FUD75 Cognitive ability and sleep loss, S1/T1 (2026-10-29): https://doi.org/10.17605/OSF.IO/AZJNX Preprint, version 1. This manuscript has not been peer reviewed. The Supplementary Material (S1–S8) is included as an appendix in the PDF.