What is the mood in Simon Vouet's painting Saint Jerome and the Angel?

In his painting of St. Jerome and the Angel, Simon Vouet a master portraitist, captured the Saint in a rather disconcerted state. St. Jerome's facial expression seems to suggest that he may be slightly frustrated by the immense task of translating the Hebrew and Greek transcripts that would form The Bible.

The Angel appears to be calming St. Jerome and the skull on the table is an indicator of St. Jerome's position as a (Latin) Doctor of the Church.