@out there:
I think its more common than you think. If you look around here you will see threads that are pages and pages long of people's experiences.
Personally, I feel that a red flag would be a therapist( not a psychologist, I mean a basic therapist or social worker) who diagnoses you with a mental illness. Therapists Im sure are good at labeling things and some know their stuff but more and more I hear about people that were told they were bipolar and after a psychiatrist visit they are told they do not, or that they have a different mental illness. That is not to say that they would be wrong or do not know mental illness just that I personally would go to someone that has actual training to diagnose mental illness.