Why does happy time pass so fast?

when something good is happening to us..
and we feel happy,
and enjoying something,
the clock runs faster than any damn thing on earth...@>@
especially when u r with someone u love ！！
but it's killing us when we waiting for somethings nice to happen,
and the clock doesnt run,
but walks sooooooooooooooo slowly,
slower than the tortoise!!