Anxiety is a state of fear usually arising from a particular cause or threat, which mayor may not be obvious to the sufferer. It is accompanied by a feeling of unease that can include physical symptoms. Its intensity varies from slight anxiousness to terror, and can consequently be acute or chronic, depending on the circumstances. Panic disorder is a state that occurs when anxiety becomes so acute and intense that it paralyses the sufferer. Panic attacks are recurrent unpredictable anxiety attacks that are of short duration but very intense, occurring among people who would otherwise not be feeling as anxious in the same circumstances.

Anxiety also takes the form of phobias, such as agoraphobia and claustrophobia; phobias are an intense fear of, and attempt to avoid certain objects or specific situations. Obsessive-compulsive disorders, withdrawal syndrome, psychoses and mental disorders also accompany anxiety, varying from slight to very intense. Anxiety is frequently linked to a psychological or emotional problem. It can be caused by an emotional conflict, a feeling of insecurity or stress, or can indicate depression. It can also be a sign of serious mental illness.

A stroke occurs when the flow of blood to part of the brain is disrupted. When this is due to a blockage of one of the arteries that supply the brain with blood, it is called an ischemic stroke. Arteries can become blocked when the inner lining of the blood vessel is damaged, allowing a blood clot to form around the diseased area. As other cells clump around the blood clot in an effort to patch up the damage, the blood vessel becomes progressively narrower until little or no blood can get through.

Less often, a stroke occurs when an artery bursts and blood leaks into nearby brain tissues. This is called a hemorrhagic stroke. If the bleed occurs beneath the arachnoids membrane (one of three layers of tissue protecting the brain) it is called a sub-arachnoids hemorrhage.

Starved of blood or swamped in it, nerve cells quickly start to die. Dying cells release chemicals that destroy neighboring cells in a cascade effect, leading to varying amounts of brain damage.