The sickness or condition you are referring to, where one's mind thinks so many things at once, is often called "racing thoughts" or "racing mind." It is a common symptom experienced by people dealing with various mental health issues, such as anxiety, manic episodes in bipolar disorder, or certain anxiety disorders.
Racing thoughts can manifest as a continuous flow of rapid and uncontrollable thoughts, making it difficult for the person to focus, concentrate, or relax. These thoughts can be unrelated, jumbled, and overwhelming, leading to heightened feelings of stress and restlessness.
If someone is experiencing racing thoughts along with other concerning symptoms, it's essential to seek professional help from a mental health specialist. A qualified professional can provide an accurate diagnosis and appropriate treatment, which may include therapy, medication, or a combination of both, to address the underlying causes and help manage the racing thoughts effectively.