What's the difference in usage between the verbs ŝajni vs aspekti?
Ŝajni emphasizes more the fact that there might be a difference between what you see and the reality.
Unhealthy is more often used in the sense of malsaniga.
The Esperanto sentence seems a little strange to me.
Does anyone else think it should be "Lia praavo aspektis malsane." or is it just me?
Both are correct. malsane modifies the verb. Malsana modifies the subject. Both lead to the same meaning of the sentences. And you can hear both variants in practical use of Esperanto.
Is there a separate word for "unhealthy"? I put unhealthy here and was marked wrong.