Acute means sudden. Acute symptoms appear, change, or worsen rapidly. It is the opposite of chronic.

Acute vs. chronic conditions

Acute conditions are severe and sudden in onset. This could describe anything from a broken bone to an asthma attack. A chronic condition, by contrast is a long-developing syndrome, such as osteoporosis or asthma. Note that osteoporosis, a chronic condition, may cause a broken bone, an acute condition. An acute asthma attack occurs in the midst of the chronic disease of asthma. Acute conditions, such as a first asthma attack, may lead to a chronic syndrome if untreated.

Ruptured intracranial aneurysm

A ruptured intracranial aneurysm causes intracranial bleeding and is considered very dangerous.