Emotions are a physical experience.
A study found that different emotions affect the body in different ways yet these effects are the same across cultures. Here, yellow shows the regions of increased sensation while blue areas represent decreased feelings.
People feel happy from head to toe, anger can literally make someone feel hot-headed and depression leaves people feeling numb. Sadness leaves the limbs feeling weak and disgust is primarily felt in the throat and digestive system.
Being in love makes a person feel a warm glow everywhere apart from their knees, perhaps hinting that there may be something in the popular saying that the object of a person's affection makes them 'weak at the knees'.