Final answer:
Hypnagogic sensations typically occur during stage 1 NREM sleep when the brain transitions from wakefulness to sleep. Stage 2 is characterized by sleep spindles and K-complexes, and stage 3 is deep sleep with delta waves. REM sleep features active brain waves and dreaming but not hypnagogic sensations.
Step-by-step explanation:
The hypnagogic sensations of falling or floating are most commonly experienced during the transition from wakefulness to sleep, which corresponds to stage 1 NREM sleep. During this stage, the brain produces alpha and theta waves signaling the transition to sleep. On the other hand, sleep spindles and K-complexes, which are important for learning and memory, characterize stage 2 NREM sleep. Stage 2 is a period of deeper relaxation where these bursts of brain activity help to inhibit processing to keep the sleeper in a tranquil state. Stage 3, commonly known as deep sleep or slow-wave sleep, is marked by low frequency and high amplitude delta waves, where it is difficult to awaken someone. REM sleep, which is not where hypnagogic sensations occur, is a phase of sleep with active brain waves similar to wakefulness, characterized by rapid eye movements and is important for dreaming and memory.