Most shrinks that I know would consider introverted to be a way of life that included a significant degree of significantly above average shyness.
Certainly my intro text treats it that way.
Needing down time—extroverts can need quiet down time.
Now I'm pretty equaled out. I LOOOOVE my ALONE time. A good book, a bowl of popcorn, no one around, some quiet music in the background...Ahhhh.
Then there is the me that shows up somewhere. I walk in the room of a party, and people proclaim "Partyman's here". Put me in a group of people, I almost always feed off the energy.
Whats funny is, I never really know what "me" is going to show up somewhere. I can go to a party expecting to be wound up and bouncing off the wall, and I end up being kind of average. THEN I can go to a party and feel kind of sub-dude and I end up being the life of the party.
At 48 you'd think I'd understand ME better. Heck, I spend less time trying to figure me out, and just go with which ever me is around at the time.
Could be — however, I return to the story of the Italian woman who preferred England because Italians were too extroverted. She was quite balanced, successful and happy and did enjoy parties and all of that, but not the extremely extroverted type. And this is what turned her away from her nation to a colder nation.