I am being treated by a psychologist or psychiatrist. When do I need to disclose this in a shidduch?

She starts from the position that a person who is currently in psychotherapy or taking medication may be obliged to disclose it, personally or through an intermediary. But when and how this is done depends on the severity of the disorder, on how much it affects one's life, and on the likelihood of difficulties in marriage. That is why each case should be assessed by competent rabbanim and professionals rather than by a general rule.

He gives general guidelines. For comparatively mild conditions, mild anxiety, mild depression, it is right to tell the person yourself when the relationship becomes serious but before anyone has had time to become fully attached. For more serious ones, clinical depression, severe anxiety disorders, cyclical mood disorders, borderline personality disorder, possibly earlier: if the condition will almost certainly interfere with normal life or with the relationship, the disclosure should be made before the first meeting; if it is successfully controlled with medication, it need not be in advance, but it must come before an emotional attachment forms.

“the disclosure should be made in advance of the initial meeting”