Mental illness, in the many forms it may take, gravely affects those who have it and all the people in their lives.  Many people who have personality disorders, substance abuse issues, and prior trauma in their lives can be living with mental illness and not even realize it.  Psychologists and psychiatrists are trained to recognize the signs and treat accordingly.
Most often a healthy diet, vitamins, exercise, good sleep, time for relaxation, and an active support system can help very much with thoughts, mood and ability to cope.   Also, having regular labs and screening tests can ensure that the rest of the body is healthy to support optimal brain function.  Medications are sometimes required in certain conditions to achieve stability.  These require close observation and often frequent adjustments to be the most effective.
I am writing about this today since 2 very close family members of mine have Bipolar disorder.  One has been living with significant year-long either manic or depressive symptoms for her whole adult life.  The other has just been diagnosed and is just starting to learn how to accept and live with his illness.  He is mostly depressed but often hypo-manic.  Both have trouble staying on their medications and both have had many setbacks.  We expect there will be many more hurdles to tackle together with love, support and compassion for the person, and greater understanding of their disease.
If you have concerns about yourself or someone in your life, please seek mental health counseling now.