I'm sure other people who have gone through more similar things could advise you about talking to your parents. The only thing I can think of is to minimize it a little. Like "I'm going through a stressful period in my life right now, and I think going to a therapist/psychiatrist/psychologist would help me develop some strategies for dealing with it more productively than I have been." Depending on your circumstances, it may not even be necessary to tell them right away. It's okay for children of any age to keep some private information from their parents.