I work in a doctor's office and can tell you first hand that a lot of patients walk in having "diagnosed" themselves on the internet incorrectly or believe incorrect information. Or old information. Doctors get annoyed with dealing with this. If a patient is so certain they are right then they should just treat themselves. That being said, I don't think researching is totally a bad thing, but you have to be careful and respect the fact that doctors have a lot of knowledge and real world experience. It's ok to bring things up but be respectful while doing it.

We once had a woman in our office call one of our doctors an idiot because she didn't diagnose her with the same thing she had diagnosed herself with. Only our doctor DID diagnose her with the same thing. The woman was using the old name for the condition that no one has used in 30 years and wouldn't except the new name for an answer!