Is regret worth?

Today I regret for a sparrow was wandering around running ceiling fan. Even I had noticed and think to turn it off but I forget. I don't care if it was my bad karma which is not important than saving a sparrow but does really a matter for saving it then it wasn't a bad karma. I'm not afraid if I've break precept or my bad krama, what else I need to pay for it. I can't revert a time neither get a sparrow alive. I don't have anything left than **regret**. Does it worth? Anything defined in sutta about regret or what Lord Buddha said about ***regret***?