I think I laugh because I find something funny. That is not necessarily the same as "feeling good". Sometimes I smile/chuckle, not because I find a joke or situation funny but because I am enjoying a person/friend or just generally grooving :-) on being in a situation; I'm content at the moment and know it. And, sometimes there is just a physical something that can get us laughing. There are whole groups of people who "deliberately" laugh for the health benefits (laugh yoga :-)