I've recently witnessed someone undergoing brain zaps and subsequent panic attacks after having stopped their SSRI medication and 48 hours partying with heavy boozing and no sleep.
Having reviewed the literature, I'm under the impression that they often occur in stress related situations or serotonin dysregulation (MDMA seems to trigger brain zaps), but I also read isolated people claiming they could voluntarily trigger brain zaps by "tensing up" and voluntary eye movements. These people said they could do that in a context devoid of any anxiety issues. Also a few marginal reports of brain zaps by heavy opiate, LSD, DXM and ketamin users, but who do not seem specific about details.
I'm under the impression that brain zaps can be caused by anxiety, but also that they can trigger violent panic attacks (fight-or-flight response from the brain zaps), but again also that they reportedly occur in the absence of stress.
What is known of what really happens at a cognitive, neural, or psychochemical level during brain zaps? What's the mechanisms? In the absence of hard science about it, what are the most plausible speculations?