Marked slowing of thought and movement typically seen in patients with major depression. This issue is also found in those people that are afflicted with bipolar disorder. One of the important things to note about this problem is that it has no physical cause; it is entirely mental. This is a great example of a somatoform disorder according to this website which also has other helpful information about the problems and causes:

Example: You ask a question and receive a blank stare for several seconds. The patient then answers very slowly. Posture is immobile.