Idiopathic hypersomnia (IH) is a rare neurological sleep disorder characterized by excessive daytime sleepiness, long or unrefreshing naps, and difficulty waking up, even after extended periods of sleep. While it shares some features with narcolepsy, idiopathic hypersomnia is a distinct condition with its own clinical profile and challenges. The journey to understanding IH has been slow, marked by decades of misdiagnosis, limited research, and evolving diagnostic criteria. This timeline highlights key milestones in the recognition, classification, and treatment of idiopathic hypersomnia. It offers a clearer picture of how far the field has come and how much more work remains.