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.
Causes of Low Blood Oxygen. The causes of low oxygen levels in blood exist in plenty - and range from illnesses like anemia to lack of oxygen in the atmosphere (the latter being quite common at high altitudes). Read on... In order to carry out various functions, our body requires a certain amount of oxygen circulating in our blood.