**Core Concept**
Reflex hallucinations are a type of hallucination that occurs in response to a specific external stimulus, such as a sudden movement or noise. This phenomenon is often seen in patients with sensory hyperexcitability or in individuals with certain neurological conditions.

**Why the Correct Answer is Right**
The patient's experience of tingling when his bed light is flashed suddenly is a classic example of reflex hallucination. This type of hallucination is thought to be related to the abnormal discharge of neurons in the sensory cortex, which can be triggered by external stimuli. In this case, the sudden flash of light may have caused an abnormal electrical discharge in the visual cortex, leading to the sensation of tingling. Reflex hallucinations are often seen in patients with conditions such as epilepsy or migraines, where the sensory cortex is hyperexcitable.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypnagogic hallucinations occur when a person is falling asleep, typically involving vivid visual or auditory experiences. They are not directly triggered by external stimuli.
**Option B:** Hypnopompic hallucinations occur when a person is waking up, often involving disorganized thoughts or visual experiences. Like hypnagogic hallucinations, they are not triggered by external stimuli.
**Option D:** Functional hallucinations are a type of hallucination that occurs in the absence of any external stimulus, often seen in psychiatric conditions such as schizophrenia.

**Clinical Pearl / High-Yield Fact**
When evaluating patients with hallucinations, it's essential to consider the context in which the hallucinations occur, including any potential external triggers. In this case, the patient's response to the bed light flash suggests a neurological rather than psychiatric cause for the hallucination.

**✓ Correct Answer: C. Reflex hallucinations**