How are drowsiness, excessive sleepiness, somnolence, hypersomnolence, and hypersomnia different?

When asked a question about a patient, I needed to clarify what exactly the problem was that was being described as “hypersomnia”. I got frustrated by trying to clarify the differences between a number of terms that seem to mean roughly the same thing—drowsiness, sleepiness, somnolence, hypersomnolence, and hypersomnia. Firstly, somnolence and drowsiness mean the…