Answer:
For example, during a heart attack.
Explanation:
Heart attack is not always identified. Some of its most common symptoms are chest pain, shortness of breath, dizziness and sweating, but they may vary. A small percentage of heart attackers don't even experience chest pain, the main sign of heart attack.
When a patient has symptoms suggestive of heart attack, he/she should immediately go to the emergency room, as every minute delay means viable loss of myocardium (the portion of the heart muscle that ensures blood circulation). The longer the delay, the greater the area of cardiac muscle necrosis and, consequently, the more severe the sequelae.
So this is a typcal case where its not possible to schedule an appointment, once its a case of emergency and the time is very important to avoid future problems.