I've posted re this article before .. The Top 5 Things Every Extrovert Should Know About Introverts.

This part got me the most ..

"4. Introverts need time alone to recharge.

Extroverts tend to think introverts have something against them as they constantly seem to refuse generous invites to social engagements. Introverts do appreciate the offers, but it’s just that they know it will take a lot of energy out of them if they pursue these social functions.

They need time alone like they need food and water. Give them their space. There’s nothing wrong with them. They’re not depressed and they’re not sad. They just need time alone to recharge their batteries."

[link to briankim.net]

Because like you I am always utterly exhausted after being around groups of people for more than 3 hours but apparently our brains are wired differently and we recharge by being alone whereas they recharge by being around people. So they think there is something terribly wrong with us that we love being alone. I've tried to explain this to family members who think I'm antisocial but they just don't get it.