This is not unheard of, in fact it may be rather common... kids may work hard to blend in, and may show a jovial outward appearance as a mask, while storing their concerns and/or inability to process the myriad stimuli. At home, in their safe space to process, they may meldtown, retreat, or shutdown.
I am uncertain how to help a child extend a sense of "safe place" to a counselor's office, other than to talk a lot at home about feelings experienced throughout the day as different things were occurring... and hope to use these conversations to build a bridge to an expert who may know more... books sometimes help with this. I will second aeh's mention of books from Magination Press (American Psychological Association). I have mentioned these several times in the forums, however that resource slipped my mind at the moment... wouldn't want to shortchange you... glad another poster mentioned them.
I'm adding a link to the related thread on
distributed learning, as the conversation on counselors has continued there.