Almost as far back as I can remember, I suffered from dreadful anxiety and nervousness. I thought it was caused by something I was imagining (psychological), but it turns out it was caused by a lack of magnesium in my diet. The anxiety seems to come mostly after eating — perhaps the ratio of magnesium to all the other nutrients in the body is not what it should be after introducing food into the body. Some foods seem to cause more anxiety than others, but I've never been able to pinpoint an exact type of food. Whatever the case, I pulled a muscle in my back one day and took some magnesium to help ease the muscle tension — coincidentally, my anxiety felt relieved. I suppose pulling a muscle was a blessing in disguise that came at the right time.
I mention magnesium because when dealing with bipolar disorder, which can be an uphill battle, you'll want as many assets as possible working in your favor. Stress build-up, which can be caused by a lack of magnesium in the diet, can thrust those with bipolar disorder into manic or depressed episodes. Whether bipolar disorder is present or not, a lack of magnesium in the diet doesn't help anybody anyway and can cause a lot of health problems.
There are many different types of magnesium. I've experimented with a lot of them. The one that works best for me is 100-350 milligrams of Magnesium Oxide after eating — depending on how big of a meal is eaten and what type of food is eaten when symptoms of anxiety and nervousness begin to appear — everybody is different and sometimes more might need to be taken. Furthermore, for whatever reason, there doesn't seem to be much consensus on why anxiety occurs after eating, although a lack of magnesium in the diet, in general, has certainly been linked to anxiety.