Painting a fleeting expression from life

I want to make a self portrait that has the spontaneity of a momentary act, like a hearty laugh or caught mid-expression.  So I did this quick study from life to see what could be done.  It has some drawing issues that can be fixed just by slowing down, but I find the biggest problem is that a laugh devolves within seconds into a pained expression. It has no half life that even remotely expresses the excitement of a true laugh.  Maybe the trick is to have Monty Python or Something About Mary on in the background to create an atmosphere that promotes easy smiles and unexpected guffaws.  I was listening to NPR (a talk about partisan politics)  on the radio and the smiles weren't flowing.  I will try it and post the results. 

Me, life size study, approx. 12"x16"