I laugh when my 4 year old daughter burst out with laughter without reason.

In childhood we laughed open heartedly without reason, as we grow older most times our pre occupied mind will not allow us to stay in present to laugh and enjoy.
Laughter lifts up our mood, vanishes the effect of the stress, relieves the physical pain, helps us to relax and recharge.

For me personally, lifts up my mood immensely and recharges me.

Laughter is a best emotion to get our head and heart in calm mode.