Acute means sudden onset within a time span of say 7 days or less. Encephalitis
mean infection of brain. Sudden onset brain infection. A big list of the causes are there. Body can loose only sensation in very few conditions like spinal cord
problems Anterior cord syndrome, central cord syndrome
or brain problems like bleeding or ischemia
. Numbness alone in 3 quarters is unheard but if its associated with muscle weakness
too, then it is called as Paresis(quadriparesis or hemi paresis or para paresis). Health supplement which would contain B-12 and Omega fatty acids might help. Hope you are satisfied with the answer. Feel free to ask any more quarries.