Shouldn’t Have Said That
This person said something to their child that they learned far too late was the wrong thing. One night, their three-year-old woke up in the middle of the night and talked to the OP about their dream. The OP did what any parent would: guide them back to their room and leave them with reassuring words before going back to bed.
However, the words they chose to convince their kid that nothing was wrong were poorly chosen. They told them that “the bugs (she dreamed about bugs) were all in her head.” The kid took that literally and couldn’t go back to sleep, thinking there was a bug infestation inside of her head.