I should be inclined to think it was from general neshness of constitution.
Wikipedia foundation.
neshness — neshˈness noun • • • Main Entry: ↑nesh … Useful english dictionary
nesh — adjective dialect weak; feeble. Derivatives neshness noun Origin OE hnesce, of Gmc origin … English new terms dictionary
neashness — obs. form of neshness … Useful english dictionary
