There are serious internal changes, too, including cardiac, metabolic and cognitive aspects. Very severe verbal and physical outbursts, extreme irritability and anger, minimal empathy and affection, marginal cooperation and general negativity unexpected for Nancy's age may actually be related to bipolar disorder.
Because impulsivity and hyperactivity are associated with bipolar, Nancy may be misdiagnosed with ADHD; so a comprehensive evaluation is critical.
This is a lifelong disorder requiring medication as well as individual and family therapy. The book, The Bipolar Child, by Demitri Papolos is an excellent resource.
As a parent, you need to educate yourself about the condition and resources to reduce its impact on your child's adjustment to adulthood. This can be a devastating disorder, especially if it's not managed competently.
Don't suffer alone. Reach out for support for yourself, your child and your family. It can be a long road even after they're adults. I don't have to remind you that you never stop being a parent.
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