Scroll down to "Information Excluded from the Right of Access", particularly the bit about psychotherapy notes.

Also see "Reviewable grounds for denial (45 CFR 164.524(a)(3))", which includes things like "The access requested is reasonably likely to endanger the life or physical safety of the individual or another person" or "The access requested is reasonably likely to cause substantial harm to a person (other than a health care provider) referenced in the PHI".

https://www.hhs.gov/hipaa/for-professionals/faq/2046/under-w...

> Another limited ground for denial exists if a licensed health care professional determines in the exercise of professional judgment that the access requested is reasonably likely to endanger the life or physical safety of the individual or another person. For example, a covered entity may deny a suicidal patient access to information that a provider determines in his professional judgment is reasonably likely to lead the patient to take her own life.

On the one hand, you might catch it and treat it earlier. On the other hand, it will color every interaction you have with others and cause stress every time you try to remember something. The potential harm may very well exceed the harm of not telling the patient (up to and including suicide).

If a doctor suspects something but lacks evidence, they may simply make a note to look for more signs at subsequent follow-ups. A patient seeing that may read more into it than is there, and subsequently suffer undue stress or paranoia.