Up to 60% of women develop insomnia during perimenopause — not because they've become bad sleepers, but because four hormonal systems that quietly managed sleep for twenty years collapse simultaneously. Estrogen destabilises the circadian clock. Progesterone loss removes the brain's natural GABA sedative. Melatonin weakens. Cortisol spikes at 3am when it should be at its lowest. Standard sleep hygiene won't fix a hormonal problem. Here's the mechanism, the patterns evidence-b