Everyone I have run into has seen my great smile. In conversation, it is easy for me to be happy or fake being happy. They both come naturally. Yet being in pain, anger or distress does not happen as naturally while I engage with others. I could be telling a sad story with very little emotion and mostly infusing it with humour. On the other hand, singing a happy song is the hardest for me.
Sad songs, melancholic poetry are easiest for me to perform and usually, the audience ask me afterwards: "Did that happen to you?" And, it does happen in the song or poetry recital. I believe that this ability comes with my personality, I am a reserved person and prefer composure. So, if a song is unhappy and sung to evoke the appropriate feelings, my audience will most likely remain composed. I want to be the singer who electrifies the audience and I use dark lyrics for that reason.
So what about happy? I think that with proper instruction, I can perform happy lyrics. Words such as 'butterfly' sound so silly on stage, I just start laughing. Even though crying and laughing are close neighbours, I don't break into extreme emotion of both while singing. Why?
Learning how to sing under various stress factors is a valuable tool. It may not be a bad idea to actually look for reason to experience these emotions and incorporate them in our singing. For some people the emotions are only controlled by switches in the brain, for others it may be not.