Lesbia, aspexi, nihil est super mi,
Quod loquar amens.
Lingua sed torpet: tenuis sub artus
Flamma dimanat; sonitu suopte
Tintinant aures; gemina teguntur
Lumina nocte."

["Love deprives me of all my faculties: Lesbia, when once in thy
presence, I have not left the power to tell my distracting passion:
my tongue becomes torpid; a subtle flame creeps through my veins; my
ears tingle in deafness; my eyes are veiled with darkness."
Catullus, Epig. li. 5]

Neither is it in the height and greatest fury of the fit that we are in a
condition to pour out our complaints or our amorous persuasions, the soul
being at that time over-burdened, and labouring with profound thoughts;
and the body dejected and languishing with desire; and thence it is that
sometimes proceed those accidental impotencies that so unseasonably
surprise the lover, and that frigidity which by the force of an
immoderate ardour seizes him even in the very lap of fruition.
--[The edition of 1588 has here, "An accident not unknown to myself."]--
For all passions that suffer themselves to be relished and digested are
but moderate:

"Curae leves loquuntur, ingentes stupent."

["Light griefs can speak: deep sorrows are dumb."
--Seneca, Hippolytus, act ii. scene 3.]

A surprise of unexpected joy does likewise often produce the same effect: