For introverts, being in a social situation - school, work, party,... - is usually very draining. We can feel flat and unfunctional from just a few hours with other people.
What do you do to unwind and recharge?
Being alone doing something that doesn't require much attention on my part, usually doing nothing. Anything that allows me to mull over what just happened. Mowing my lawn is actually very good for me, 5 hours of mindless mowing and half-heard music.