Basically, the main differences between sleep and unconsciousness have
to do with the way the brain deals with information (from both
internal and external sources) and the kind of response (if any) that
is given in reaction to changes in that information. A sleeping person
will rouse if a loud noise or other unusual event occurs; an
unconscious person will not. In the depths of unconsciousness, very
little information processing occurs; there are no thoughts or dreams,
no signs of self-awareness, and even a painful stimulus may not bring
the person to a state of alertness. Consciousness is a continuum, and
the boundaries between wakefulness, sleep, unconsciousness, and coma
are not hard-edged.
Here's a good (if brief) list of some differences between being asleep
and being unconscious:
"A. Difference between being asleep and being unconscious
1. brain continues to process external information
2. brain continues to process internally generated information
3. body remains active
4. in general, easily awakened"
Sue Ann Kelley, Ph.D.: Consciousness
More online info on the subject:
"Sleep... is defined in the Stedmans Medical Dictionary as 'A
physiologic state of relative unconsciousness and inaction of the
voluntary muscles, the need for which recurs periodically'. Totora &
Grabowski in Principles of Anatomy and Physiology add that 'it is a
state of unconsciousness from which a person can be aroused;
associated with a low level of activity in the reticular activating
Learning Discoveries Psychological Services: What Is Sleep?
"Breathing emergencies also come in different forms, the person can be
conscious or unconscious, breathing on their own or not. It is very
important to determine whether the person is conscious or not;
sleeping is NOT unconscious. A good way to find this out is to nudge
the person or tickle their feet. If they move around and can be
aroused you will then know they are sleeping. If it is found that the
person is not responding to anything that means they are unconscious."
Essortment: Breathing emergencies
"Sleep is defined as a state of unconsciousness from which a person
can be aroused. In this state, the brain is relatively more responsive
to internal stimuli than external stimuli. Sleep should be
distinguished from coma. Coma is an unconscious state from which a
person cannot be aroused. Sleep is essential for the normal, healthy
functioning of the human body. It is a complicated physiological
phenomenon that scientists do not fully understand. Historically,
sleep was thought to be a passive state. However, sleep is now known
to be a dynamic process, and our brains are active during sleep."
eMedicine Health: Basics of Sleep Introduction
"In medical textbooks, unconsciousness is typically divided into four
subcategories: obtundation, hypersomnia, stupor, and coma. Obtundation
is simply a reduced level of alertness/consciousness, similar to the
confused state with which you awaken from a sound sleep. Hypersomnia
is a very deep sleep from which you can only be awakened by vigorous
stimulation. Stupor is deep unconsciousness from which you can only be
aroused briefly using noxious or painful stimuli. Coma is deep
unconsciousness from which you cannot be awakened at all--truly
Fire EMS: Unconscious, Unresponsive, or Underestimated?
"Coma is a prolonged period of unconsciousness. Unconsciousness is the
lack of appreciation of (or reaction to) a stimulus. Coma differs from
sleep in that one cannot be aroused from a coma."
While You Are Waiting: Understanding Coma
"Levels of unconsciousness vary from a very light state, in which
movements or even protesting sounds are made when the unconscious
person is disturbed or subjected to pain, to a state of deep
unconsciousness (called coma) in which even the strongest stimuli
bring no response."
NHS Direct: Unconsciousness
Google search strategy:
Google Web Search: "being asleep and being unconscious"
Google Web Search: "sleep and unconsciousness"
Google Web Search: "levels of unconsciousness" + "sleep"
Thanks for an interesting question. If anything needs clarification,
please don't hesitate to ask.
Clarification of Answer by
02 Aug 2004 16:39 PDT
Dreaming, as it is commonly understood, does not occur in comatose
patients (nor in those who are under deep anesthesia). However, I can
testify that certain incoherent, visionary imaginings can pass through
the mind of a comatose or deeply anesthetized person. It happened to
me many years ago. My experience did not resemble a dream, since it
didn't have a "plot" or any recognizable people or things in it. It
was more like a surreal screensaver that my brain was generating to
keep from slipping deeper into blackness.
Here's an excellent article about the causes of coma:
Newfoundland Brain Injury Association: Understanding Coma
Regarding how easy it is to slip into a coma, normally it isn't easy
at all, unless drugs or injury are involved. Fortunately, people who
"pass out" generally become conscious, rather than drifting into coma.
Oh, and about "Six Feet Under": I taped it, and haven't watched the
tape yet, so please don't tell me too much!
Clarification of Answer by
02 Aug 2004 17:39 PDT
As I mentioned, consciousness is a continuum. There aren't clear
guidelines as we drift from one state to another. Generally, a person
who has "passed out" (from alcohol use, for instance) will provide
some responses, even if full wakefulness is not reached. Poke a pin in
someone who has passed out, and he or she will probably flinch; a
comatose person doesn't respond to pain. "Smelling salts" (usually
ammonium carbonate) may rouse a person who has passed out, while a
person in a coma can inhale the vilest of substances without giving a
reaction. Note, however that poking pins in a person and exposing him
or her to smelling salts may make the person really ticked off at you
when they do wake up. ;-)