Continuous subcutaneous EEG recordings from 20 healthy adults across a full year reveal that sleep architecture is meaningfully shaped by environmental and social factors. Early summer brought shorter total sleep time and reduced REM duration. Bright sunshine shortened sleep latency, while heavy cloud cover lengthened it. Higher temperatures advanced sleep timing and suppressed deep sleep. Weekend nights reliably delayed sleep onset, offset, and midpoint, with Sunday nights showing altered architecture — a pattern consistent with social jetlag, which affected a meaningful minority of participants. No robust multi-day intrinsic sleep cycles were detected.
The finding matters because most sleep science relies on one- or two-night laboratory polysomnography, which cannot capture the slow drift in architecture driven by seasons or cumulative lifestyle patterns. This dataset — arguably the longest continuous EEG sleep record in healthy humans — confirms that REM and deep sleep are not fixed biological constants but fluctuate with light exposure, ambient temperature, and social schedules across months. For adults, the actionable implication is clear: consistent sleep timing through weekends and attention to bedroom temperature during summer may protect the most restorative sleep stages. Limitations are significant: only 20 participants limits generalisability, sqEEG captures fewer channels than clinical polysomnography, and this is an observational cohort unable to establish causation. As a preprint posted to bioRxiv and not yet peer-reviewed, these findings should be treated as preliminary until independent validation confirms the seasonal and meteorological effect sizes.