How can you tell if your sleeping cat is in the non-REM (deep sleep) stage?
Cats and humans experience identical sleep stages, but with different timing. Humans enter REM or “rapid eye movement” about once every 90 minutes. Cats attain this state once every 25 minutes when they are sleeping.
During REM sleep, owners often say their cats are “chasing” something in their dreams. This is a reference to the cat’s physical behavior, which includes eye movement, whisker twitching, slight paw movement, and minor vocalizations.
Cats who are not in REM sleep are perfectly still. This does not mean, however, that they have no dream activity. All mammals begin to dream as soon as they fall asleep, but the dreaming that occurs in that less active state involves recent events from the day.
The dream activity in REM sleep is more intense because it draws on a store of memories that can go back years. Cats are capable of impressive feats of both short and long-term memory. They also have object permanence, which means they continue to understand that objects exist even if they can no longer see the item in question.
It is perfectly normal for cats to move in and out of REM sleep just as humans do, they simply cycle into the state more clearly, and its presence, or absence is clearly recognizable.