Instances of when schizospectrality and complex dissociation influence eachother
A few come to mind on my own experience. Feel free to add your own.
On ipseity disturbances in particular:
It is well known in PTSD that watching a traumatic event or knowing somebody going through a traumatic event can be traumatizing itself. When the line between the self and the other is blurred, as they are in schizospec disorders, watching something traumatic happen to someone else can feel the same as watching it happen to you. Social disconnection, such as feeling like a passive observer in life, which are also common in schizospec disorders, can increase this; when you are a passive observer in the things that already happen to you, what is the difference between something happening to someone else?
There is also the fact that the minimal self, which what the disturbance in 'ipseity disturbance' is, well, disturbing, is understood as the 'fundamental' or 'building block' to the narrative self, which is the part which is disturbed in trauma. The foundations themselves are shaky, and it is easy to see how that can lead to the narrative self being easier to fragment. The tendency for rumination on what one's self is and various topics that ipseity disturbances frequently lead to more opportunities for traumatically instilled beliefs to fester; when one is constantly hyperreflecting on the nature of oneself in relation to the world, there are just more chances for the "conclusions" or realizations from introspecting to end up being trauma-related. When interaction is a game that constantly leads to being related back to oneself in an attempt to understand oneself, trauma-related beliefs may end up being more frequently reinforced or triggered as well.
There is also that hyperreflectivity may aim itself towards trauma. It is common in complex dissociation to have a pressured sense "I must figure out everything that happened to me," and prodding dissociative barriers in this way when not ready can lead to a worsening of that dissociative structure. In terms of answering the question "What is my self, what does that mean?", when trauma forms the basic lines of what divides and defines the differend selves, the pressure to figure it all out can increase, leading to more rumination.
Keep in mind all the previous on ipseity as a constant weight in the background of all of this.
In socialization, schizospectrals are frequently othered, isolated, or ostracized for their experiences, or the vague sense that something is off or that you are "crazy." Isolation itself worsens schizospectral symptoms in general, but it can also worsen dissociation; if you are alone, and you already generally find more comfort in your internal world than the external world, you have more time to draw inward and continue relying on dissociative mechanisms to survive. This can influence complex dissociation both positively and negatively: I find I am drawn to spend more time with my alters, and thus that increases integration and communication, which has even led to fusion before. Negatively speaking, the overreliance on dissociative coping mechanisms eventually weakens other coping mechanisms, which can give rise to a more complex system structure, reinforce the need for certain pre-existing dissociative structures and make them harder to dismantle and integrate later when they are no longer needed, and the nature of being constantly alone or other itself can become a key part of trauma and thus system structure.
The increased paranoia and guardedness around socialization can become a chicken-and-egg situation for trauma and schizospectrality. Somebody with complex dissociation has faced severe trauma to know it is possible and remain so hypervigilant in day-to-day life; this can feed into delusions and the constant pressure of double bookkeeping delusions to remain functional can cause several problems. When you live in two worlds simultaneously - the world where your paranoias are true and the world of shared reality you assimilate into - you are using a form of dissociation as a coping mechanism. You are sorting yourself and the world into two different experiences - having to constantly do this can create new alters in itself to hold psychotic experiences or chance system structure. Alters who are unable to doublebookkeep consistently may be more dysfunctional, may not be allowed to socialize and thus increase their feelings of otherness or isolation, and alters who are able to double bookkeep consistently may begin to strain more under the constant stress.
Internal confusion between what is psychotic and what is dissociative:
In the minute to minute experience of life, when you hear a voice, you're just hearing a voice. To recognize an alter and distinguish it from random psychotic noise requires a level of knowledge and/or integration with the alter or fragment that spoke. How do you know who to aim for to integrate, how do you know what can be ignored?
There is a nature of self-gaslighting when living with psychosis. You learn to not trust your senses and to double-check with others, which can compound trauma as it leads to being vulnerable to the gaslighting of others. Self-doubt and denial is a core feature of complex dissociation already (denial is a form of mental flight and can serve to maintain dissociative barriers between parts), and in cases of complex trauma in general there is a sense that you are your only advocate already. When you cannot trust yourself, it is just harder to foster trust between your different selves. Doubt and suspicion drives alters further apart, but doubt and suspicion are core mechanisms to surviving with psychosis.
Ignoring dissociative parts as "just psychosis" for long enough can have drastic consequences: the last thing a traumatized part wants when coming forth with trauma is to be dismissed. Mentally pushing away a part like that is a method of increasing dissociation - thus, mistaking parts and psychosis can have drastic consequences on system functioning. Alters can and will develop further on their own without actively communicating towards other parts; in my case, I have pushed away an entire layer of my system as just psychosis for years, and only recently reconciled with them: what would have remained at most 1-10 parts is now sitting at a firm 30-ish with three subsystem divisions and an alter who has 8 fragments within themselves to manage. It had also had the effect of pushing them into psychosis: many of them face delusional misidentifications that the other part of our system projected onto them. One layer believed we were hallucinating these things, and thus the other layer begun to believe they truly were those things, which delusionally strengthened the substitute beliefs that the other layer formed with as adaptations.
Furthermore, there being evidence for the capacity for others to harm you also leads to confirmation bias as evidence towards delusions. When I saw my first psychiatrist, when I had expressed constant fears of being sexually assaulted the first question asked was "Have you experienced that before?" (and I have) - it's another chicken-and-the-egg situation. But also, when the knowledge of what severe harm can come your way is more expansive like it is in a complex trauma survivor, more out-there or bizarre experiences can feel more likely. When you go day to day as a psychotic you learn a baseline level of psychosis to cope with, and as psychosis gets worse, that baseline can increase; things that are bizarre become more neutral. These two feelings can work together to make even "obviously" bizarre delusions feel more likely to be real. You have already gone through so much in consensus reality, thus the upper limit on what is factually possible to happen to you further becomes blurry with when it extends into the impossible. (There is an extensive discussion here on how OEA often uses the idea that it is too bizarre or impossible to possibly be real to create self-doubt in survivors and to get away with further abuse, and how TBMC in particular can mimick psychosis to an even larger extent than complex dissociation in general is already conflated with psychosis. But I am not an OEA survivor, and that is not my discussion to begin.)
Again, these are just a few mechanisms I've noticed in my own experience; I'm sure there's more thought to be put into each, and more that I haven't thought about. I'd like to further think about certain kinds of parts and how they form due to and around psychosis (especially delusional misidentifications and how they overlap with introjects and/or nonhuman alters), but I don't have that figured out to the extent that I feel comfortable writing about it for others to read, for instance. And again-again, feel free to add your own.