Definition reprinted with permission from Culebras, Antonio, Clinical Handbook of Sleep Disorders, Butterworth-Heinemann
The imagery and thinking experienced during sleep. Sleep mentation usually consists of combinations of images and thoughts during REM sleep. Imagery is vividly expressed in dreams involving all the senses in approximate proportion to their waking representations. Mentation is experienced generally less distinctly in non-REM sleep, but it may be quite vivid in stage 2 sleep, especially toward the end of the sleep episode. Mentation at sleep onset (hypnagogic reverie) can be as vivid as in REM sleep.