Problem Relevance The COVID-19 pandemic has become a challenge for the world at all levels, from individual to population one. The introduced restrictive measures of self-isolation, observation and quarantine, which were usually known to healthcare professionals only before the pandemic, have become the forced forms of lifestyle for most people in different countries — their specific «becoming accustomed» to new, unusual, conditions of existence and communication. Some of these conditions (sensory and information deprivation, perceptual isolation, etc.) attracted the attention of clinicians in the last century [1]. However, living in unusual conditions has been studied mainly in military medicine (within the framework of space, Arctic and marine medicine), since the second half of the 20th century [2, 3, 4]. A number of works demonstrated, in particular, that numerous disease-causing factors underlie the development of mental pathology in unusual living and communication conditions: a specific and usually long-term stressful situation («unusual» life, information deprivation, etc.), the asthenizing factors of professional activity (monotonous work, disturbance of the usual sleep-wakefulness rhythm, hypodynamia, etc.) and individual features of the group (team) members, their psychological compatibility with each other [4, 5]. These factors, taken together, often led to the development of painful manifestations: from preclinical (periodic emotional fluctuations, transient super-valuable and obsessive thoughts, etc.) to expanded, clinical mental disorders, usually at the borderline (neurotic) level [5, 6]. In some particularly severe cases, the states of confusion and other psychotic manifestations were observed.
The mental state of people during infectious epidemics has been actively studied since the second half of the 19th century. In particular, the review of the flu epidemic in 1889 demonstrated a wide range of mental disorders among sick and recovered individuals: from dyssomnia to neurotic disorders, persistent depressive states and even suicides. During the influenza pandemic in 1919, K. Menninger also noted psychotic disorders, which occurred, according to him, in more than half of the 1,000 patients he examined [7]. Research conducted by British scientists during local outbreaks of coronavirus infections in recent decades (SARS and MERS) demonstrated that they were accompanied, besides sleep disorders (54 %) and depressive disorders (42 %), with the states of confusion (36 %) and persistent (after discharge from hospital) asthenic symptoms [8].