Because menopause is a natural stage of life it's less about a "diagnosis" and more about identifying whether or not the symptoms you are experiencing are related those of menopause. It can be difficult to distinguish the hormonally-based symptoms of menopause from more general changes during this time of life, such as children leaving home, changes in relationships or careers, or the death or illness of parents. These events can also cause sleeplessness, stress and anxiety, much like menopause can.
With all the possible explanations for your symptoms, how do you know if it's menopause?
A discussion with your doctor will let you know for sure, but the "official" transition into menopause is when you have not had a period for 12 full months. Hot flashes, night sweats, irritability, occasional sleeplessness, weight gain, decreased sex drive, fatigue, and poor concentration are some symptoms of this stage of life. As a rule of thumb, you are likely to start menopause at approximately the same age as your mothers and sisters. There's a good chance that you may have already been experiencing symptoms (during perimenopause), but as you enter menopause they may become more frequent or intense.