It is physically impossible to sneeze while you are asleep.

Sneezing is a complex reflex involving the coordinated effort of several muscle groups. When you enter Rapid Eye Movement (REM) sleep, the brain releases neurotransmitters like glycine and GABA. These chemicals trigger a state known as REM atonia, which effectively paralyzes most voluntary muscles to prevent you from acting out your dreams.The sneeze reflex requires the activation of the diaphragm, intercostal muscles, and muscles in the throat and face. Because these muscles are suppressed during sleep, the physical mechanism for a sneeze is unavailable. Even during non-REM sleep, the sensory nerves in the nose are significantly less sensitive to external stimuli.Research from institutions like the University of Pennsylvania's Sleep Center indicates that the 'sneeze center' in the medulla oblongata is less responsive during slumber. If an irritant such as dust or strong perfume is powerful enough, it will trigger the trigeminal nerve to send an emergency signal to the brain. This signal forces the body to transition from sleep to a wakeful state.Once you are awake or in a very light stage of arousal, the paralysis lifts and the reflex is restored. This is why you might wake up suddenly and immediately sneeze. This biological safeguard ensures that the body remains still during rest while still maintaining a defense mechanism against respiratory irritants.