In contrast, Manser says, a person's passive vocabulary consists of the words whose meanings they knowâso that they do not have to look the words up in a dictionaryâbut which they would not necessarily use in ordinary conversation or writing (The Penguin Writer's Manual, 2004).
Sleep Apnea, Night Terrors, and Nightmares. Sleep apnea may also be to blame for your nightmares. During sleep apnea, your brain senses the low oxygen and realizes that you are under a very real threatâyou are being choked or smothered by your own bodyâand if nothing is done you will die.
Monitoring Your Blood Oxygen Levels. If your doctor discovers that your blood oxygen level (oxygen saturation) is less than about 90% during the day (when you are resting), then your oxygen levels are probably dropping during the night. This means that you have sleep apnea, or other respiratory disorders, like UARS.