You know what they say…fake it ’till you make it. In this case it actually holds true.
Smiling is an automatic response to happiness. Whenever we feel good or there’s something funny it automagically appears on our faces. But research shows it actually works both ways. The physical act of smiling triggers feelings of happiness. And it doesn’t work just with smiles. Assuming a confident pose actually makes us feel more confident for example.
So if you’re feeling a little down try consciously smiling at every little thing that you know is supposed to make you smile. Eventually (pretty soon actually) it will start feeling more natural, until good mood is restored.