neurosthenia

Etymology 1
From New Latin, from + ;.

Noun

 * 1)  Strong reaction or overreaction of a nerve to a stimulus.

Etymology 2
From mistaken rebracketing of (whose valid surface analysis is ) as if it were prefixed with, by false analogy with most other ISV compounds beginning with the syllable neur- + /ə/ (which are thus prefixed). The error is not rare, but it invites proscription because the -a- syllable in neurasthenia corresponds to the negation of strength, that is, to weakness (of constitution or affect); by surface analysis, it is equivalent to a- ("without"/"opposite"), the difference between strength and weakness.

Usage notes
Because the error makes the word neurosthenia nearly contranymic and may suggest (to a careful reader) either carelessness or ignorance on the writer's part, replacing it with the intended word, neurasthenia, is a good way to avoid any reproach.