**Core Concept**
Sleep disturbances are a common symptom in various psychiatric and medical conditions, and accurate diagnosis is crucial for effective management. The International Classification of Sleep Disorders (ICSD) provides a framework for diagnosing sleep disorders.

**Why the Correct Answer is Right**
The correct answer is based on the clinical assessment of sleep patterns and symptoms. The diagnosis of sleep disturbances involves a thorough history, physical examination, and sometimes polysomnography (PSG) or actigraphy. Clinicians use standardized questionnaires and rating scales, such as the Pittsburgh Sleep Quality Index (PSQI), to evaluate sleep quality and identify potential sleep disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a diagnostic tool or approach. While sleep diaries can be helpful, they are not a comprehensive diagnostic method.

**Option B:** This option is incorrect because it is too vague and does not reference a specific diagnostic criterion. Sleep disturbances can be caused by various factors, including medical conditions, medications, and lifestyle habits.

**Option C:** This option is incorrect because it is incomplete. While PSG is an important diagnostic tool for sleep disorders, it is not the only method used to diagnose sleep disturbances.

**Clinical Pearl / High-Yield Fact**
When evaluating sleep disturbances, clinicians should consider the patient's medical history, medication use, and lifestyle habits, as these factors can contribute to sleep disorders.

**Correct Answer:** D. Clinical assessment, including history, physical examination, and standardized questionnaires.