(((((((Petunia)))))))

I hope I didn't alarm you! I really don't think it's anything to worry about, I have never heard anything that says nightmares (and the symptoms that go with it) can cause any type of physical harm. I just thought if it concerned you then it would be a good question for your doctor.

Cortisol is a stress hormone that gets released into the bloodstream, but I believe that it can be harmful only if it's a constant thing. (Like not taking time for yourself when you're under great amounts of stress). I don't think a nightmare is a long enough duration for us to really be in any danger. I do know that dreaming is supposed to be good for us, no matter if it's a good or bad dream, since it supposedly helps rid our subconscious of excess "waste." I am not qualified to give advice on the question you asked, I was just stating a thought. I'm sorry if I caused you any worry!

Love,
Sujin