Things that are hectic tend to be happen quickly and all at once — that's why a hectic day makes people nervous.
Think about a calm, beautiful island with the sun shining and nothing to do but read a book. That kind of peacefulness is the opposite of hectic. When things get hectic, people sometimes say things are getting crazy or bananas: events are happening too fast for us to keep up, so we tend to get agitated or even angry. Because there's so much work to do, being a student is often a hectic job.