Sleep/wake patterns were recorded by continuous 24-hour ambulatory polysomnography in 339 patients, who had episodes of altered consciousness. Patients were recorded while they were outside the hospital. From a seven-channel montage of electrodes affixed below the hairline, sleep polygraphic EEG was easily read from T3-T4, EOG from F2-F8 and EMG from T3-T6. Sleep was staged by analysis of aural signals on 60 times real time playback, augmented by continuous visual display and selected frozen frames. Patient major sleep period patterns reflected those reported for general populations. Unexpectedly, 47% of the patients took daytime naps and 44% of the nappers took more than one nap. Naps had a mean duration of 71 minutes. Those who took no naps slept significantly longer at night by 23 min. Napping reduced night sleep much more in patients who did not take CNS-acting medications. We conclude that excessive sleepiness may in part explain complaints of episodically altered consciousness.