I killed a family of strangers... and laughed

I had a dream where it was raining and I was in a trench coat, I had a butcher knife and a gun..I walked up a dark hill and walked into a house I do not recognize nor the people inside.. there was a family of four people and (2 girls 2 boys) I shot the 2 girls in the head first and then I did some very gruesome things to the men with the butcher knives then whipped the blood off with the eldest man's tie and walked out of the house I then I just felt a jerk and I woke up laughing like it was funny and laughing for real not nervously and I haven't had a dream like that since but It really freaked me out help!!!