lethargy

Concise Oxford English Dictionary © 2008 Oxford University Press:
lethargy /ˈlɛθədʒi/

▶noun

• 1 a lack of energy and enthusiasm.

• 2 Medicine a pathological state of sleepiness or deep unresponsiveness.

– derivatives
lethargic adjective,
lethargically adverb.

– origin ME: via OFr. from late L. lethargia, from Gk lēthargia, from lēthargos ‘forgetful’.