Smiling Is a Disease

They say that laughter is the best kind of medicine,
And a day without laughter is a day wasted 
But what about a simple smile? 
Is it really as contagious as they say? 
Smiling is a good way to make people believe you're actually happy when you're not
A mask that's pretty to the eyes and warms the heart
A sweet and caring way of showing your love and happiness
Or at least that's what it's supposed to mean right? 
Then how come when I smile, sometimes I feel the need to hold back tears? 
Smiling is a disease that makes me feel better when I'm really not...