Easy. The classic of the genre is an induced delusional disorder, when a sick person with delusions, who has influence in the family, infects his / her spouse, child, other relatives with his ideas. And in the end, sometimes it is not clear: who is sick, who is the root cause.
You will be surprised, but up to a certain point both the person himself and his environment may not notice the developing mental pathology or not attach such importance. This happens, first of all, because the majority of people in our country are psychiatrically illiterate, inclined to believe in idle speculations, prejudices of a painful historical past, which, unfortunately, have become widespread delusions; they have a poor idea of what mental illness is - in their obscurantism people tend to deny and fear everything unknown, while psychiatry is still covered with a gloomy halo of mystery. According to many, it is shameful to be sick with a mental disorder. People are not just not aware of the processes of their own mental life, they are still superstitiously afraid of words in which there is a Greek prefix "psycho", denoting only the concept of "soul". Denial is a common mechanism of psychological defense, therefore, the first thing that most often a person who feels that certain changes are taking place in his psyche will begin to convince himself of the opposite. (There are, perhaps, exceptions - subjects with hypochondriacal disorder, for example). Such denial may be a subconscious desire of a person to protect his self-esteem, self-perception of his personality from the blow when he realizes his own striking difference from other, "normal" people and feels shame and guilt for his own "inferiority". Relatives of patients behave according to the same principle, who in most cases negatively perceive even a hint of a mental disorder in a person close to them and sometimes deny even objective observations. If the changes in the psyche are really serious and strongly interfere with the normal life and the usual functioning of the individual, but at the same time the person is able to realize that what is happening to him goes beyond the mental experience of most of the people around him (i.e. none of them like did not experience), that is, the likelihood that sooner or later he, of his own free will, will seek the help of a specialist in order to restore mental health. However, it should be understood that with many gross mental disorders, despite the strange and inappropriate behavior, the person, on the contrary, loses criticism of his condition - the denial of the disease is no longer so much a protective mechanism as a symptom of the disease itself. This is the so-called anosognosia, when a person is unshakably convinced that his painful ideas absolutely accurately reflect the actual reality, the sick person ceases to realize the severity of his condition, he does not understand that he is sick, or does not believe in it. Most often, it is at this stage that the disease becomes noticeable to the immediate environment, which, with unpleasant surprise and misunderstanding, discovers that their relative or friend is performing pretentious, unusual actions (for example, they can express ideas of persecution, says that the special services are spying on him, or refuses from food, because she believes that she hasTranny taste and they decided to poison it). In this case, a person's ill health (even if he himself is firmly convinced and convinces everyone that he is healthy) becomes obvious, and then, thanks to the assistance of loved ones, he falls into the field of vision of psychiatrists - but this is at best, and at worst he is led to healers, psychics and exorcists. It happens in another way. When the disease develops gradually, gradually, it is not always noticeable that the oddities in a person's behavior are due to mental problems, this is usually not assumed in the first place. The people around him may think to the last that a person is simply tired, that is why he began to drop out of social life, or that his interests have changed, so he dropped out of university, or that he is a lazy and weak-willed whiner who cannot pull himself together, so he lies intact facing the wall for days and refuses even to clean the room. Others are able to come up with many excuses for unusual behavior, depending on the degree of whimsy of their fantasy, but often their assumptions are wrong and only further distance a person from understanding that he really needs qualified psychiatric help, otherwise the disease can take on a difficult and / or protracted course. In any case, if there are suspicions about one's own or someone else's mental illness, the decision to come to a consultative, preventive conversation with a doctor of the appropriate profile and resolve your doubts will be universally correct. This is not something to be afraid or ashamed of.
Quite! In today's world, we are used to not seeing something that cannot be considered normal at all, given common sense. And common sense is different for everyone. Deviations are one thing and can be easily overlooked. And diseases and pathology are completely different and it is impossible not to notice it. We often do not see complexes and serious "quirks" of people until we see them in one or another fatal (or not so) situation.