droop         
verb [ I ] uk/druːp/ us/druːp/
 下垂,下弯
to bend or hang down heavily
  The flowers were drooping in the heat. 花朵在热浪中垂下了头。 
 I can see you're tired because your eyelids have started to droop. 我能看出你累了,你的眼睛都快睁不开了。 
  垂头丧气,沮丧
If your spirits (= feelings of happiness) droop, you start to feel less happy and energetic.