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.
What are the causes of a low blood oxygen level? The body's tissues get oxygen from red blood cells, but when a person's red blood cell count is too low, tissues are deprived of a certain amount of oxygen. Many symptoms associated with anemia are caused by lowered oxygen in the blood.