Rule 522 The party claiming that any person, including himself, is or was insane has the burden of proof on that issue.

If you want a court to consider that someone is or was mentally ill, you have to prove it. This applies whether you are making the claim about yourself or about someone else in the case.

This means the court starts by assuming everyone involved is mentally competent. You cannot simply raise the idea of insanity and expect the other side to disprove it. The responsibility falls entirely on the person making that claim.