Likewise. I fall into both camps depending on where I am and who I'm with. I can party like the best of them (probably better!) but also take a week or two a year to go and spend some time with myself, somewhere remote, and just spend the time catching up on some reading, walking in the countryside, writing, taking photographs and just being.
Like black/white, left/right, maybe there's some middle ground? Or maybe, like perversion, it's a matter of relativity? Some uptight individuals think anything other than sex in the 'missionary' position is perverted. I used to share a house in my youth with an very very camp gay man, who was so extroverted than anyone else, no matter who, seemed introverted when he was about!
Although at the end of the day, does it really matter? If you're happy in your skin, then that's what counts.