When you visualize things you are no longer focused in reality but instead in your own world its people's "happy place". and thats why visualization promotes relaxation and stress reduction.
Appetite is not linked to hunger since appetite is the activity and drive in order to eat whereas hunger is the physical and mental state in which a person needs to eat.
Also appetite is linked to many unhealthy behaviors that can result to other symptoms of eating disorders which causes deletrious effects on one's mental and biological state.
The importance of measuring and documenting vital signs for patients is because they are the baseline of health of that patient. It can tell a healthcare professional if the person has a trend of hypertension (high blood pressure) or tachycardia (increased heart rate). It can tell if someone is febrile which can tell if someone has an infection.
Knowing the baseline vitals will help diagnose and properly treat a patient. Without knowing what the baseline vitals of a patient is, it can be dangerous to the patient if a healthcare professional treats them. For example, if a patient is presenting with chest pain in relation to a heart attack, the healthcare provider will need a set of baseline vitals in order to give that patient nitroglycerin (a medication to open the vessels). The top number (systolic) of the blood pressure must be greater than 90mmHg. Without knowing the initial blood pressure of the patient and giving the nitroglycerin, the healthcare provider would risk dropping the blood pressure dangerously low and likely killing the patient.