Anxiety Disorder

Differences between anxiety and anxiety disorder
Usual anxiety comes from an association of a neutral event or object (e.g. exam revision) and another fearful or unpleasant event or object (e.g. failing an exam). When these two events or objects are repeatedly paired with each other, we may think of failing an exam whenever we start exam revision. Thus, when we start revision, we might also experience the fear and anxiety of failing the exam, or later even associate to failures in other events (failures in other aspects in life) or catastrophized outcomes. We name this type of fear or anxiety as "Fear Conditioning".
The worry of failing the exam, on one hand, may drive us to prepare better for the exam, yet on the other, overwhelming fear may lead to overthinking or even inability to concentrate.
Adaptive anxiety
When facing threats, anxiety or fear, serving as a basic survival instinct, may help us with adapting to the environment. Optimal fear helps to protect us from harm, and prepare us to face or avoid dangerous events or situations. For example, we might be scared when we are high up, thus, to adapt to that particular environment, we become extremely careful, hold onto the handrail tightly, or leave the place as soon as possible to prevent falling.
It is common to feel anxious when we face foreseeable threats. When we are in face of something we fear or something we do not of full grasp of, we often experience stress, anxiety and fear. Physiologically, our nervous system would respond to these stresses, and prepare the body to either fight or flee from the threat. These responses are what we called "fight-or-flight mechanism”.
Besides, the cortisol level (also known as the stress hormone) would increase when we are facing stress, leading to some bodily responses, i.e. increased heart rate, sweaty palms.
Generally speaking, the anxiety and physiological responses usually would not last long. They would usually be automatically regulated by the body, or would subside when needs are fulfilled.
Fight-or-flight mechanism
Fight-or-flight mechanism is a normal reaction towards a perceived harmful situation in all animals. Take a deer as an example:
When a deer is searching for food in plains and comes across its major predators, what do you think the deer will do?
Run away:
It will leave the scene at once. This refers to "flight" in fight-or-flight mechanism.
If the lion is rather young and weak, the deer may fight back. This is known as "fight".
When it is impossible to run away or fight back, surrender or playing dead become the choices left. This response is known as "freeze".
When we decide to run away or to fight back, we have to prepare our body beforehand so as to run faster or to fight more fiercely. Thus, the heart pumps faster to transport energy to our four limbs, and our digestive system will be temporarily suspended, so that the energy could be fully utilized by the body parts which are responsible for making moves. This is also one of the common physiological reactions found in humans when facing threats.
However, our perceived threats in real life are not our perpetrators, but something we worry or anxious about, i.e. work, family, relationships etc.
Physiological reactions:
Muscles tension, increased heart rate, sweating, shortness of breath or upset stomach etc.
Emotional reactions:
Anxiety, Worry
Cognitive reactions:
Worry of danger, being out of control or negative happenings
Behavioural reactions:
Prepare for future threats, including solving problem, escaping from danger etc.
What is General Anxiety Disorder?
Maladaptive anxiety
When worries or fearful responses prevent us from adjusting to situations, we call it maladaptive anxiety.
When we are facing too much uncontrollable worries, we will react to it with "fight-or-flight mechanism" and be in a state with high level of stress hormones. If we are chronically in this state, "stress hormone" will constantly trigger physiological reactions such as increased heart rate and muscle tension. Prolonged exposure to cortisol also weakens the immune system and in turn affects our health and daily functioning.
As mentioned before, when we experience excessive unrealistic anxiety and fear which further leads to dysfunction of automatic adaption, we might have developed anxiety disorder.

Daily worry/fear vs Anxiety Disorder
Take up a shorter period of time, may last for a few hours to a few days. Take up most of the time in every week, usually last for more than six months
2. Level of worry/fear
Controllable Overwhelming negative thoughts and excessive worries and fears
3. Influence
Do not interfere with daily life Affect daily life, for instance, worsened job performance and relationships, impaired concentration and decision making ability, sleep problems etc.;
Certainly, the level and duration of fear vary among individuals, it is hard to generalize and the above table act only as a reference. Should you have any enquiries, please contact related healthcare professionals (e.g. psychiatrists, clinical psychologists).