HCRT and neurodegenerative disease: In this review, we summarise recent research on the impact of sleep and circadian rhythm alterations in ageing and major neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, and frontotemporal dementia, highlighting the roles of melatonin, orexin, and melanin‐concentrating hormone (MCH) systems as key regulators at the intersection of sleep and neurodegeneration.