
I didn’t know the answer right away so I had to do some reading on the subject. I’m still not a 100% sure, but no, the body is not in fight-or-flight mode (also known as acute stress response) during a nightmare. Bad dreams are classified as nightmares when they wake a person up from sleep (without the waking, it is only a bad dream). Since your body is in REM sleep when you are dreaming, it is also in a state of paralysis. Your brain is producing higher levels of certain neurotransmitters, which could correlate with the fight-or-flight response, but the majority of your voluntary muscle groups are paralyzed. So you wouldn’t be able to fight…or flight.
Anyone else have some information on the topic?
Here is an amazing video on dreaming.