The pronounced caution towards claims for injury to the nervous system is founded on two, far from negligible, considerations. First is the fear that to treat psychiatric injury on the same wide lines as external injuries from physical impact would open up 'a wide field for imaginary claims'. There used to be, though now waning, scepticism in judicial minds concerning the degree of reliance which can safely be placed on medical diagnosis both as to the existence of such trauma and its causal connection with the defendant's conduct. Mental injury is more easily simulated than external injury, and exposure of counterfeit claims rendered difficult by the time lag between accident and trial. This apprehension goes far to explain why the courts soon modified their opposition to nervous shock as a head of 'parasitic damages', consequential to some other tort, like bodily injury from actual impact. It also makes intelligible their categorical refusal to permit recovery for mental suffering, unaccompanied by objective and substantially harmful physical or psychopathological consequences: mere fright, anguish or grief is deemed too trivial, evanescent or easily faked unless it either accompanies some external injury (when it will readily qualify as but another of the scrambled strands composing the conventional item of 'pain and suffering') or constitutes a causal link with some later external injury, as when alarm impels the plaintiff to jump off a high platform. Otherwise emotional shock must amount to 'physical injury' or, more precisely, it must have resulted in some organic damage, like miscarriage, coronary thrombosis or stroke, or in severe psychiatric injury like hysteria or anxiety neurosis (particularly 'post-traumatic stress disorder' - PTSD). There must be a sudden assault on the nervous system (hence the traditional reference to 'nervous shock', not just an accumulation of stress or grief).