ICD-10 Code F51.19 – Other hypersomnia not due to a substance or known physiological condition (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code F51.19 – Other hypersomnia not due to a substance or known physiological condition
What it is
F51.19 identifies hypersomnia, or excessive sleepiness, when it is not caused by a substance, medication, or a known physical condition. Use it for sleepiness that is documented as a primary sleep disorder or otherwise unexplained.
Clinical signs
Clinical features vary; refer to documentation. Common findings include prolonged sleep time, repeated daytime sleep episodes, or difficulty staying awake despite adequate opportunity for sleep.
When to use this code
Use this code when the record describes hypersomnia and the clinician rules out alcohol, drugs, or an underlying medical cause. It also fits cases labeled as other or unspecified hypersomnia when the documentation supports a non-substance, non-physiologic cause.
Code only when the provider clearly documents the condition. If the note suggests narcolepsy, sleep apnea, depression, or another defined disorder, choose the more specific diagnosis instead.
Do not use for
Do not use F51.19 for sleepiness caused by medication, substance use, or a medical disorder. Check documentation if the chart points to narcolepsy or another specific sleep-wake disorder.
Coding tip
Confirm that the provider has excluded substance use and known physiologic causes before assigning this code.