The absence of epinephrine during REM sleep allows for the experience of emotionally laden events without fear or anxiety, facilitating unlearning.

“So if a car suddenly screeches in front of us or we get a troubling text message, adrenaline is deployed into our system. Adrenaline is epinephrine. Those are equivalent molecules. And epinephrine isn't just released from our adrenals. It's also released within our brain. So there's this weird stage of our life that happens more toward morning that we call REM sleep, where we're hallucinating and having these outrageous experiences in our mind. But the chemical that's associated with fear and panic and anxiety is not available to us.”