Babies have this comfort zone of how many people they want to be around. If they grow up with lots of people around, they suddenly feel at a loss when they are alone. If they are used to just having their parents around, they feel overwhelmed when they are around many people for a long time.
I've noticed it with many 2nd generation indian kids who go back to India on vacation. They flip out when they first get there, because they're suddenly being doted on by grandparents, uncles, aunts, and cousins. Three or four weeks later, they head back home and are suddenly antsy when only their parents (and maybe siblings) are around.
I think that happened to me this month. I've been working alone for the past nine months and was suddenly thrust into three weeks of meeting people (though I actually didn't do the normal amount of socializing because I was pretty busy working).
Now I'm back in Berkeley, and working from an empty, quiet home again seems awfully difficult.