Final answer:
Hypnagogic images are experienced in stage 1 of sleep. They are hallucinations or vivid sensory experiences that occur during the transitional phase between wakefulness and sleep.
Step-by-step explanation:
Hypnagogic images are experienced in stage 1 of sleep. Hypnagogic images are hallucinations or vivid sensory experiences that occur during the transitional phase between wakefulness and sleep. These images are often associated with stage 1 sleep, which is characterized by the appearance of theta waves and a marked slowdown in both respiration and heartbeat.