Bipolar Disorder is a mood disorder that is characterised by alternating periods of mania and depression. It was formerly known as manic depression. People with Bipolar Disorder can swing from extreme highs to extreme lows, sometimes very quickly. This can often feel confusing or even frightening for the sufferer and their loved ones. It is often treated and managed by a combination of medication and psychotherapy. In the first place it might be appropriate to have a psychiatric assessment to establish the diagnosis, suitable medication would follow from this. A GP would supply a referral to an appropriate psychiatrist. It might be helpful to speak with a therapist while you work through an understanding of the experience.
http://www.nhs.uk/conditions/Bipolar-disorder/Pages/Introduction.aspxU
