ICD-10 Code F51.1 – Hypersomnia not due to a substance or known physiological condition (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code F51.1 – Hypersomnia not due to a substance or known physiological condition
What it is
F51.1 identifies excessive sleepiness or prolonged sleep that is not explained by a substance, medication, or a known medical condition. Use it when the chart documents a primary sleep disorder rather than secondary hypersomnia.
Clinical signs
Typical documentation includes daytime sleepiness, prolonged sleep episodes, or difficulty staying awake despite adequate opportunity for sleep. Clinical features vary; refer to documentation.
When to use this code
Use F51.1 when the provider diagnoses hypersomnia and rules out alcohol, drugs, or an underlying physiologic cause. It may also fit when the note describes recurrent excessive sleepiness without another specified sleep disorder. Check documentation for the exact clinical reasoning.
Do not use for
Do not use this code for hypersomnia caused by medication, substance use, or a medical disorder. If the record points to narcolepsy or another specific sleep diagnosis, code that condition instead.
Coding tip
Confirm that the provider has excluded substance-related and medical causes before assigning F51.1.