Optimally a parent seeking custody is not mentally ill at all. Unfortunately, life doesn’t work that way; people who are (more or less) blameless for their mental illness often need help to overcome it.
If you are fighting with the other parent or a guardian (or whoever) for custody of your child(ren) and you are alleged to be a person in need of psychiatric treatment, then you should probably seek it. If the allegation is false or is greatly overstated then your counselor can come testify to that fact or offer a report to the court and thereby undermine an important part of the argument against you. If a professional concurs that you do need treatment you can obtain the treatment and undermine an important part of the argument against you.
Generally, in my experience with family court, if you are, in fact, mentally ill:
- Everybody who’s going to testify thinks you’re mentally ill, and will generally, under cross-examination, admit to those elements of your behavior and to past incidents that reinforce that narrative, even your mother; your attorney will attempt to get them to “explain away” the behavior in a way that doesn’t undermine your case, but it won’t be as effective as you want because the objective facts are damning while the “explaining away” is self-serving;
- Lots of your past behavior, behavior that seems reasonable to you and which you can explain to your own satisfaction and that of your close friends, can be cast in a way that will illustrate your illness even if the behavior or incident is actually unrelated to your mental illness;
- There is usually an audio recording (usually a message left on a phone, but very often a video) of you saying something that sounds mentally ill or threatening, and the judge will hear that, and;
- Your denials will generally be ineffective since your even your mom admits to your crazy behavior.
However, all is not lost. Overcoming mental illness by taking responsible action actually creates a useful narrative for court purposes: (e.g.) you have, because of the strength of your character, obtained the help you needed, overcame a substantial difficulty and you will use that same character to guide your children. The testimony of the counselor you sought out when you were confronted or accused of mental illness will generally be very credible and your counselor is generally very sympathetic to you as well. The alternative narrative is that of the unstable person who is in denial and refuses to get help. Which person would you rather have raising your children? This is the sort of thing a judge has to decide when confronted with allegations of mental illness when they are required to make a custody decision. This kind of narrative is something you have to consider if you’re fighting over custody.