As another person who has trouble being "on" all the time, when I'm at a high-social-pressure event, I always take time off to be by myself. Often I go off for a walk somewhere for a couple hours, or if I've got a particularly gripping book, just sit in my room and read.

Even when I chaired Mythcon, and could not drop from sight for extended periods, I would take breather intervals to curl up in a corner and decompress.