Medical literature robustly supports a close link between sleep disorders and psychiatric disorders. Recently, the co-occurrence of sleep dysfunctions and psychotic experiences (particularly insomnia with paranoia) has been reported, although the causal relationship is still unclear  . Moreover, Reeve et al.  have observed as insomnia, nightmares and circadian phase delay are associated with an increased occurrence of subsyndromal psychiatric symptoms in young people.
In this paper, we report an emblematic case of co-occurrence of sleep and psychiatric disorders in one of the most influential writers of the 20th century: Franz Kafka (Prague, 1883-Kierling, 1924). He was affected by tuberculosis, but, as reported by Felisati et al.  , mental more than physical diseases have influenced his life and literary work. The main information on Kafka′s health emerge from the large collection of private correspondence and diaries that were published after the writer′s death. From “Diaries”  and “Letters to Milena”  emerge: an insecure, frail, anxious and depressed personality, a distorted and unstable self-image, a gloomy relationship with his family, friends and loved women, a man living a state of alienation from the outside world and having a self-destructive tendencies. According with 5th edition of Diagnostic and Statistical Manual for Mental Disorders (DSM-V)  , these impairments in self and interpersonal functioning and the presence of pathological personality traits (as emotional lability, anxiousness and depressivity) suggest that Kafka could have suffered from a borderline personality disorder with co-occurring anxiety and depression. Moreover, from “Letters to Milena” clearly emerges that the writer suffered from insomnia. Kafka wrote: “ I have had increasing insomnia” and “ my health is good, just that I don′t sleep well” . The write knew the sleep′s importance and he lived his insomnia as a guilt: “sleep is the most innocent creature there is and sleepless man the most guilty”  . It is difficult to classify Kafka′s insomnia. We suggest that the causes have to be searched in his lifestyle and in his mental disorders. The writer deliberately did most of his intellectual work at night. This choice depends primarily on Kafka′s persuasion that writing in a sleep-deprived state provides access to otherwise inaccessible thoughts. From “Diaries” seems to emerge his fear of falling asleep: “my insomnia only conceals a great fear of death. Perhaps I am afraid that the soul, which in sleep leaves me, will not be able to return”  . This tendency to worry excessively about sleep, the hyper arousal and the anxiety suggest that Kafka could have suffered from a psychophysiological insomnia. It is a very prevalent form of insomnia not caused by an outside stressor but due to a learned response that teaches the subject to not fall asleep when planned  . Learned anxiety and heightened arousal of sleep represent both precipitating and perpetuating factors in the development of psychophysiological insomnia  . Bastien et al. have observed signs of cortical hyper arousal in individuals suffering from this form of insomnia  .
As previously suggested, Kafka could have suffered from borderline personality disorder. Some studies have shown that this personality disorder is with sleep disorders  ,  and  . Particularly, a significant decreased sleep time, a decreased sleep efficiency  , longer sleep onset latency, more sleep arousals, more frequent nightmares and awakenings  have been reported in individuals suffering from borderline personality disorder.
We conclude that Kafka′s case may represents a clear example of co-occurrence and link between sleep and psychiatric disorders, particularly between borderline personality disorder and psychophysiological insomnia.