drowsy vs half asleep

drowsy

adj
  • Causing someone to fall sleep or feel sleepy; lulling; soporific. 

  • Dull; stupid. 

  • Boring. 

  • Inclined to drowse; heavy with sleepiness 

half asleep

How often have the words drowsy and half asleep occurred in a corpus of books? (source: Google Ngram Viewer )