It all depends on the disorder itself. First of all, I would like to note that Maxim Iln noted an important factor - heredity. True, it has not been proven for all disorders. In the case of schizophrenia, this is 50/50, according to twin studies. The statistics will differ depending on the disorder.
Mental disorders have such a phenomenon as "premorbid" or premorbid personality state. For example, on approaches to the first episode of schizophrenic psychosis, a person may experience the following symptoms:
narrowing the circle of communication;
unwillingness to leave the apartment;
self-care skills deteriorate;
But the same can be with, for example, depression. And depression can be with bipolar disorder and ... everything is confusing.
Simply put, if you notice that your personality is changing, you should pay attention to it.
At the same time, your standard behavior may be similar to the premorbid of schizophrenia, and then everything is very difficult.
It is best to pay attention to how you feel and whether you are satisfied with what is happening to you most time or basically there are unfounded anxieties, fears, a feeling of unreality of what is happening and / or oneself.
It will be easiest when voices arise. Here you definitely need to go to the doctor, but there is no need to talk about prevention. In this case, everything has already started.
Nevertheless, some markers can be captured by studying your thinking. For example, in schizophrenia, the categorization of objects is based on latent features. I now divide applications on the phone according to their functional characteristics, scattering them among daddies. And you can arrange them according to the principle of a color palette, where one color flows smoothly into another. The presence of such features may indicate a potential start of a mental disorder in the near future. At the same time, it can be nothing more than show off. This also happens and therefore it is not worth making hasty conclusions.
If you think you are sick, I recommend visiting a psychiatrist and pathopsychologist. They will be able to more fully study your condition and adequately answer all questions, taking into account all the controversial points about which I wrote above.
And the last thing - it can be difficult for a patient to track the onset of the disease. I have seen only a couple of such cases when a person understood that what was happening to him was unreal and was a symptom, and then he sought help. Criticism of one's state of psychosis is not preserved.
According to modern psychiatry, any chronic psychotic disorder, with rare exceptions, is more biologically determined, that is, hereditary prerequisites are necessary, conducive to certain disorders in the work of higher nervous activity.
That is, this form of psychosis cannot be prevented (at least at the present stage), you can only help a person to adapt to its presence and to some (sometimes significant) degree to stop symptoms with the help of medications and psychotherapy, first of all.
There is also such a thing as acute psychosis - or "psychotic breakdown" that arises as an individual reaction to some particularly traumatic events. In this case, you can engage in preventive measures, in particular, work on resistance to stress and increasing the tolerance of strong affect; this reduces the likelihood that potentially traumatic incidents can shock the psyche and upset it to the degree of psychosis.
The symptoms of psychosis themselves are primarily positive (i.e. in the sense that something absent in the norm , arises) phenomena: delirium (when a person is 100% sure of something radically unreliable for a mentally healthy person) and hallucinations (false images of perception and sensation generated by a disordered psyche). Also included are often mood disorders (depression, mania) and negative symptoms (impaired attention, thinking, memory, etc.).
And as a conclusion - a similar fear, the fear of "going cuckoo" before level of psychosis, has a specific name, phrenophobia. And it belongs to the category of neurotic disorders. From the point of view of clinical observations, the owner of such a mental illness, most likely, is unlikely to have psychosis (although it is not completely excluded).