I am very familiar with MPD, and what you describe isn't it. People who suffer from multiple personalities experience distinct changes, and often times are unaware of them. Each personality often has its own name, and its own set of memories. In many cases, the personalities do not communicate with each other without very intensive therapy. MPD can be brought on by abuse, but other traumatic childhood experiences can trigger it as well. Currently, MPD is not completely curable, but those aflicted with the psychosis can, in many cases, lead relatively normal lives if properly treated.
How do I know this? My father was an MPD. It was a bizarre childhood for me and my two brothers, waking up each morning wondering "Who is daddy going to be today?"
What you describe sounds very much like a form of bi-polar disorder (manic depression). There are tests that a competent psychiatrist can give to determine if this is a correct diagnosis. If so, there are many medications available on the market to control the mood swings and accompanying disorientation.
Please visit a competent physician or psychiatrist for a correct diagnosis. There is no more shame in suffering from a psychological ailment than there is in suffering from a physical one. The world of medicine has made extraordinary strides in the field of mental health in the past decade. You can live a life of relative normalcy.
How do I know? I am bi-polar. I have been on medication for more than a decade. Although I still have mood swings, they are not as debilitating as they once were. Even though mental illness carries a stigma with it, and I know I am taking a chance by "outing" myself as a bi-polar, if it will encourage someone else reading this to seek treatment, then it is worth it. Besides, thanks to my "illness", I have led a far more interesting life than I likely would have had I been born "normal".
