Fast thinking, or "racing thoughts," is most commonly known as a symptom of the clinical psychiatric disorder of mania (and of the manic part of bipolar disorder or "manic-depression"). But, according to
Princeton University psychologist Emily Pronin, most healthy people also have experienced racing thoughts at some point in time -- perhaps when they are excited about a new idea they have just learned, or when they are brainstorming with a group of people, or even when they lie in bed unable to fall asleep.