I go through phases, or as I refer to them, 'swings'. I'll NEED to be around and with people sometimes.. an extroverted swing, where I get cabin fever easily from my daily routine.
And I go through introverted swings as well, where I don't really want to be around anyone, and I'd be perfectly content in my own little world on my own.
The introverted ones tend to last longer, but the extroverted swings are a bit more intense. I don't really control when they come up, and they don't happen on any regular basis that I can notice myself.
Anything between that is normal. If I have people to be around, I'm content, and when I don't, I'm content as well.