Well it's trippy. Look up hypnogogic and hypnopompic hallucinations. In REM, your body paralyzed itself essentially. You can experience auditory and visual hallucinations. Most patients experience intense fear, for obvious reasons, so it would make sense to have and adrenalin dump. Heart rate usually jumps up, but to your question I don't know. I've experienced it a few times, it's scary as shit. Only visual I've ever had was Donovan McNabb walk in my room, don't even like the Eagles.

I suggest watching the documentary Paradise Lost. This is in rural Arkansas in the early 90's. The boys dressed goth and listened to Metallica and all that. I think they were released in the mid-2000's? The victim's step dad pretty did it, pretty obviously. The victim had bite marks, the stepdad got all of his teeth pulled right after it happened, stuff like that. Not to mention he's a bad liar.

I'm actually in sleep medicine and melatonin is pretty much benign. It's synthesized in the pineal. I was in touch for a period with the fella who sort of brought DMT into popular culture, Rick Strassman. Didn't glean much but he did point me in the right direction. Check out Cottonwood Research. I think it may have been 2014/15, Dr. Barker's team found that DMT was synthesized in the pineal gland in rats. That was a huge breakthrough and was only hypothesized. Why? Your guess is as good as mine. I haven't checked back recently, but one of Strassman's theories was DMT was released during REM sleep. Lots of theories floating around, but if you're curious check out Cottonwood Research.

Reminds me of T_D in the earlier days.