Bipolar disorder is also known as manic depression. It's a mental illness that causes extreme mood swings, so that the person suffering from the disease experiences extreme highs and severe depression, as frequently as every day, or over several months. The disease appears to be triggered by stressful events, although once the cycle is triggered, it doesn't stop. A bipolar patient averages eight to ten manic or depressive episodes, but some experience more, and the cycles are neither regular, nor predictable.
Symptoms of the depressive phase include sad mood, fatigue, weight loss or gain, decreased ability to concentrate, difficulty making decisions, thoughts of suicide, or sleep problems such as insomnia, excessive sleeping or shallow sleep with frequent awakenings. The acute manic phase is marked by feelings of grandiosity, being easily distracted, racing thoughts, talking too much, and insomnia. Some of these are similar to the depressive phase, but they are accompanied by high energy instead of low energy.
Scientists disagree on what causes bipolar disorder. It is probably hereditary: the relatives of someone who is bipolar have a higher likelihood of also suffering from the disease. Studies have shown that in people with bipolar, some areas of the brain contain more neuron cells than other areas, resulting in overstimulation by chemicals released by those neurons, known as neurotransmitters. But the exact role neurotransmitters play in bipolar disorder is still unknown.