The defining symptoms of fibromyalgia are chronic, widespread pain and painful response to touch (allodynia). Other symptoms can include moderate to severe fatigue, needle-like tingling of the skin, muscle aches, prolonged muscle spasms, weakness in the limbs, nerve pain, functional bowel disturbances,[14] and chronic sleep disturbances.[15] Sleep disturbances may be related to a phenomenon called alpha-delta sleep, a condition in which deep sleep (associated with delta waves) is frequently interrupted by bursts of alpha waves, which normally occur during wakefulness. Slow-wave sleep is often dramatically reduced.[citation needed]
Many patients experience cognitive dysfunction[16] (known as "brain fog" or "fibrofog"), which may be characterized by impaired concentration,[17] problems with short[17][18] and long-term memory, short-term memory consolidation,[18] impaired speed of performance,[17][18] inability to multi-task, cognitive overload,[17][18] diminished attention span, anxiety, and depressivesymptoms.[18] "Brain fog" may be directly related to the sleep disturbances experienced by sufferers of fibromyalgia.[citation needed]