What are some main symptoms that preexist and worsen in psychotherapy or any similar form of counseling?

It depends.: It depends on the issues that bring a person to therapy. In general terms, therapy seeks to invite alternative perspective and thinking about the sensory perceptions encountered. To embark on this process of change may stimulate the very emotions and defense mechanisms being addressed. The skill and wisdom of the therapist modulates this dilemma. Long term solution to long term problem.

Dealing with trauma: A patient coming to therapy for help dealing with a traumatic event might temporarily experience worsening symptoms. This regression would be due to the necessity of recalling specific details of the traumatic event, making a cohesive narrative from these memories, and integrating the associated overwhelming feelings into conscious awareness. It's the latter part that can feel worsening.