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 symptoms of low oxygen? Symptoms of low oxygen levels in the blood include rapid breathing, fast heart rate, confusion, shortness of breath and changes in the skin color, which can range from blue to cherry red, according to WebMD. Body tissues require a certain amount of oxygen for the body to function properly, notes Mayo Clinic.