What idea did Charley have about the tunnel and why didnt he tell the psychiatrist about it in the lesson third level by Jack Finney?

Charley felt there was a tunnel that nobody knew about, which was feeling its way under the city at that moment too, on its way to Times Square, and maybe another to Central Park.

Grand Central, he felt, was like an exit, a way of escape and perhaps that's how he got into the tunnel.

He didn't want to tell the psychiatrist, for he would not have believed him and would have wanted to treat him.