What Is The Difference Between Hyper Aerated And Hypo Aerated

What is the difference between hyper aerated and hypo aerated lungs? My sons xray says he has focal airspace disease and the lungs are hypo aerated. He is in a great deal of pain and was in the hospital for 6 days with viral meningitis. He is home now but can't sleep flat, laugh or take a deep breath and we've been out if the hospital for 4 days. Should I be worried?