Hi Jamie and welcome to NeuroTalk.

I’ve not heard specifically of holosync meditation, but I do practice mindfulness meditation which I find helpful. I doubt if any form of meditation would be harmful.

Studies using fMRI imaging showed increases in neural synchrony – the integration of localized neural processes into higher order cognitive and emotional functions with meditation, decreasing feelings of anxiety and improved feeling of empathy. Other benefits observed included a decrease in the emotional reactivity that can worsen mental distress, which many of us have experienced following a TBI.

While it's not specifically about meditation with TBI/PCS patients, a good discussion on this can be found in “Pictures of the Mind: What the New Neuroscience Tells Us About Who We Are” by Miriam Boleyn-Fitzgerald.

"OM" to you