Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an awareness of self and environment or to respond to any human or environmental stimulus. Unconsciousness may occur as the result of traumatic brain injury, brain hypoxia (inadequate oxygen, possibly due to a brain

infarction Infarction is tissue death (necrosis) due to Ischemia, inadequate blood supply to the affected area. It may be caused by Thrombosis, artery blockages, rupture, mechanical compression, or vasoconstriction. The resulting lesion is referred to as a ...

cardiac arrest Cardiac arrest (also known as sudden cardiac arrest CA is when the heart suddenly and unexpectedly stops beating. When the heart stops beating, blood cannot properly Circulatory system, circulate around the body and the blood flow to the ...

), severe intoxication with drugs that depress the activity of the central nervous system (e.g.,

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

and other hypnotic or sedative drugs), severe

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

pain Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...

anaesthesia Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prev ...

, and other causes. Loss of consciousness should not be confused with the notion of the psychoanalytic unconscious, cognitive processes that take place outside awareness (e.g., implicit cognition), and with altered states of consciousness such as

sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...

, delirium, hypnosis, and other altered states in which the person responds to stimuli, including trance and psychedelic experiences.

Causes

This is not a complete list.

Cardiovascular system

* Arrhythmia (irregular heart beat) * Bleeding *

Cardiac arrest Cardiac arrest (also known as sudden cardiac arrest CA is when the heart suddenly and unexpectedly stops beating. When the heart stops beating, blood cannot properly Circulatory system, circulate around the body and the blood flow to the ...

* Cardiomegaly * Heart failure (HF) (congestive heart failure (CHF)) *

Myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...

(MI) (heart attack) * Myocarditis * Pericarditis * Shock

Nervous system

* Brain abscess *

Brain tumor A brain tumor (sometimes referred to as brain cancer) occurs when a group of cells within the Human brain, brain turn cancerous and grow out of control, creating a mass. There are two main types of tumors: malignant (cancerous) tumors and benign ...

* Encephalitis * Increased intracranial pressure * Intracerebral hemorrhage (hemorrhagic stroke) * Ischemic stroke *

Meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasion ...

* Seizure *

Subarachnoid hemorrhage Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid (brain), arachnoid membrane and the pia mater surrounding the human brain, brain. Symptoms may include a thunderclap headache, severe heada ...

* Traumatic brain injury (TBI) (intracranial injury)

Respiratory system

* Acute respiratory distress syndrome (ARDS) * Choking * Drowning * Lung cancer (lung carcinoma) * Pneumonia * Pulmonary embolism (PE) * Respiratory arrest * Respiratory failure

Other

* Drugs * Electrocution * Kidney failure * Liver failure *

Poison A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

Sepsis Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage of sepsis is followed by suppression of the immune system. Common signs and s ...

Law and medicine

jurisprudence Jurisprudence, also known as theory of law or philosophy of law, is the examination in a general perspective of what law is and what it ought to be. It investigates issues such as the definition of law; legal validity; legal norms and values ...

, unconsciousness may entitle the criminal defendant to the

defense Defense or defence may refer to: Tactical, martial, and political acts or groups * Defense (military), forces primarily intended for warfare * Civil defense, the organizing of civilians to deal with emergencies or enemy attacks * Defense industr ...

of automatism, i.e. a state without control of one's own actions, an excusing condition that allows a defendant to argue that they should not be held criminally liable for their actions or omissions. In most countries, courts must consider whether unconsciousness in a situation can be accepted as a defense; it can vary from case to case. Hence epileptic seizures, neurological dysfunctions and sleepwalking may be considered acceptable excusing conditions because the loss of control is not foreseeable, but falling asleep (especially while driving or during any other safety-critical activity) may not, because natural sleep rarely overcomes an ordinary person without warning. In many countries, it is presumed that someone who is less than fully conscious cannot give

consent Consent occurs when one person voluntarily agrees to the proposal or desires of another. It is a term of common speech, with specific definitions used in such fields as the law, medicine, research, and sexual consent. Consent as understood i ...

to anything. This can be relevant in cases of

sexual assault Sexual assault is an act of sexual abuse in which one intentionally Physical intimacy, sexually touches another person without that person's consent, or Coercion, coerces or physically forces a person to engage in a sexual act against their w ...

euthanasia Euthanasia (from : + ) is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different Legality of euthanasia, euthanasia laws. The British House of Lords Select committee (United Kingdom), se ...

, or patients giving

informed consent Informed consent is an applied ethics principle that a person must have sufficient information and understanding before making decisions about accepting risk. Pertinent information may include risks and benefits of treatments, alternative treatme ...

with regard to starting or stopping a medical treatment.

References

{{Consciousness Consciousness Symptoms and signs of mental disorders