So it's not some new, modern form of hypnosis?
Not at all. You're fully awake and aware the entire time. In fact your active participation is required.
Basically the therapist will have a special light that has a string lights side by side in a line. They set the speed of the light (somewhat fast) and you sit a number of feet back from it.
Keeping your head still you follow the light with only your eyes, this is the part that simulates REM during sleep.
The therapist then will give you basic instructions, telling you to think on a certain element of your trauma. That's it.
Doing this in 10 min increments 4-5 times per session should begin unlocking the trauma.
The therapist I had that told me about it said she used it on a client she had who'd been kidnapped and locked in a car trunk for a day. She had severe PTSD and could barely sleep.
After 2 sessions with EMDR she made huge, life changing leaps in her recovery and healing.
It has a high success rate with PTSD.
It also requires a special class and certification, so not all counselors, etc... are trained in it.
Despite not having trauma I tried it a few times (as it supposedly has other uses as well, for some). It didn't help me, hence only a few tries, and I not having the conditions it's focused on, but I found nothing harmful or concerning about its use, spiritually. I spent a week researching it before even attempting it as I, too, had my doubts, but it came up safe sounding there, as well.