I saw this study.
Apparently some sleep problems are genetic.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3157659/
Sleep Reactivity and Insomnia: Genetic and Environmental Influences
Quote:
Our results provide strong evidence for the heritability of sleep reactivity to stress in both insomniacs
and non-insomniacs and add to the growing literature suggesting that insomnia has significant genetic determinants.
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