There are side effects with rTMI and they can be very serious, however, they are not typical. Side effects include: Headache, Scalp discomfort at the site of stimulation, Tingling, spasms or twitching of facial muscles, and Lightheadedness [0]. Serious side effects can include: Seizures, Mania, particularly in people with bipolar disorder, and Hearing loss if there is inadequate ear protection during treatment [1].

Particularly in the issues around PTSD that was induced alongside cranial trauma, rTMI is an unlikely treatment, though still viable. The issue is that PTSD and concussions share strong co-morbidities. If you have a concussion, your physician is more likely to suggest other treatments, as rTMI may cause other issues. In reading through the literature, I cannot find a case where an issue was seen, but I can understand the caution with such a new technology. That said, there may have been cases that I am unaware of. I'll be very clear here, I am not a medical doctor. If you are considering rTMI treatment, please see a physician.

[0] https://www.mayoclinic.org/tests-procedures/transcranial-mag...

[1] https://en.wikipedia.org/wiki/Transcranial_magnetic_stimulat...