I have a 16 month old that is showing of signs of becoming this way. The only time she is truly happy is alone in her playpen. She comes at 7 and is fine till everyone is here and then every little thing is just more than she can bear and she cries. She doesn't always sleep up there just lay and talk to herself. But it is also effecting her afternoon nap of course cause she did nothing to make herself tired just rested so for two weeks now we have been not letting her go to bed and just making her cope and it can get pretty noisy but she needs to learn other ways of coping which means find a place to play that no one else is. I made sure I have some corners and hiding spots available so she has options. The mom was talking about how she has been acting when they visit grandma - an aunt and two cousins live there too and it is the same there so at least I know it isn't just daycare. She stays in moms arms for the first hour they visit then plays only when mom is there to play too. Up to a month ago there were never any issues playing with the group and it's all the same kids. So just a quirk she will need to get over - no napping just support to cope.