The experience the governess describes here is symptomatic of what was formerly known as hysteria. This quintessentially female malady was the bane of the 19th century: according to Rachel Maines, doctors found symptoms in 50-75% of all women. These were extraordinarily vague and formed an almost limitless list. Difficulty sleeping, anxiety, tics, sexual arousal, inattention, irritability and faintness were all sufficient to incur a diagnosis.
The origin of the condition was thought to be repressed sexual desire and its prevalence in Victorian society reflects the fact that female lust was itself seen as a pathological aberration. In James's time, it was treated by what was euphemistically referred to as 'pelvic massage', which a doctor would administer either digitally or by using a jet of water or clockwork vibrator. That the medical profession was apparently oblivious to the resemblance of the 'hysterical paroxysm' to orgasm highlights how unthinkable female sexuality was.
With the rise of psychoanalysis, the repression entailed in hysteria was increasingly viewed as the result of a split consciousness. Henry James would have been well-informed on this subject as his older brother, the prominent psychologist William James, wrote extensively about hysteria. His declaration — "if there are devils, if there are supernormal powers, it is through the cracked and fragmented self that they enter" — is highly pertinent in this context and illuminates the way that Henry James presents the supernatural and psychological as co-existing, rather than mutually exclusive, forces. The idea that hysteria is allied with sexual repression, meanwhile, ties in with the governess's sublimation of her attraction to her employer.
Watch an interview with the brilliant Rachel Maines, a historian who has written extensively about hysteria:
It is also worth remembering that James wrote The Turn of the Screw very shortly after Sigmund Freud and Josef Breuer published their seminal Studies on Hysteria in 1895. In particular, the case of 'Lucy R.', a 30-year-old governess of two small children, has such strong parallels with the novella that it may have been a direct inspiration. 'Lucy R.', like James's governess, sublimates an unacceptable love for her employer into that for her young charges, whose mother she subconsciously wishes to replace. There are other smaller details, such as a purloined letter and paranoia about the other servants, which also suggest this study informed James' work.