The ability to require the other side to provide documents or answer questions is known as "discovery".
Discovery in court cases is often limited by various legal protections such as relevance or communications being "privileged." Generally, mental health records are "privileged" (protected) and need not be disclosed.
In M.M. v. L.M., 2012 Pa. Super. 195 (2012), Father suffered from severe bipolar disorder and had been hospitalized multiple times. He had violent tendencies and even attacked maternal grandfather during a custodial exchange. The parties entered into a consent order of court granting Father supervised custody. However, he also executed a release for medical records stemming from his most recent hospitalization so that the judge could review them.
He later consented to allow Mother to depose his psychiatrist as well (though the deposition never occurred). Father was subjected to psychological evaluations. However, Mother requested that she receive the actual hospitalization records. Father objected due to his privacy concerns as the upcoming psychological evaluation would be a less intrusive tool to adduce his mental health status.
The trial court compelled Father to provide this documentation. However, the Superior Court reversed the trial court, explaining that Father's voluntary hospitalization was privileged and could not be compelled. The Superior Court agreed that an updated psychological evaluation is less intrusive.
In custody proceedings, the prevailing standard is the best interests of the child. However, even in cases where a parent has mental illnesses and a propensity for violence (which are certainly relevant in this determination), the court must still respect a parent's right to privileged communications. Health (HIPAA) privileges and other privileges may be waived (lost) or not asserted. It is important to find a family law attorney who knows the law of privilege and how it intersects with custody law.