The Doctor’s Growing Concern

When the doctor first saw baby Tom, he didn’t see any cause for concern. The baby appeared perfectly healthy, and he assumed it was just another case of a new mother being overly worried.
However, Sally was adamant that something was seriously wrong with her son. She told the doctor that she had kept him in the sink for an entire day. This statement made the doctor pause and grow more concerned. What exactly did she mean by that?