I read somewhere that introverts and extroverts have batteries, but they charge them in different ways. An extrovert's battery is charged when they are the center of things, when they are in a crowd and loving it. An introvert, however, needs solitude in order to recharge their batteries.
It's a pretty good analogy, and I feel that it is definitely accurate. I am an introvert, and even when I'm around a small group of close friends, I get to a point where I would prefer to go home, cuddle up in bed and read a book or veg in front of the TV and watch something from my Netflix cue. Get me around a larger group of people, and I hit that threshold pretty soon - and it's no longer a preference, but a strong urge. I would go so far as to say that I'm quite miserable after an hour in a large group.
Most people don't get this need for solitude, this feeling of emotional exhaustion after having talked, smiled, and socialized for long periods of time. I even feel a bit abnormal, although I know people just like myself. It's just introversion, that's all. I am very blessed to have married a husband that a) is not a party animal, and b) understands me and my need for solitude, most of the time. I love being around him, and often miss him during the day, but sometimes if I've been home all day and still don't feel like doing much of anything, he wonders why I feel the need to stay cooped up.
Sometimes, my batteries need a longer charge, that's all.