Emotional, sad.?

I am always sad. If i have thoughts of something sad, ill be sad for the rest of the day most likely. i cry to the abnormal amount when hearing the song Christmas Shoes, i cry at the sight of almost anything else crying. The weird thing is, horror movies do not upset me. When i see someone one screen killing someone else, i do not cry. I have told myself i know its fake. but if i know horror slasher movies are fake, why do i cry watching titanic or some other depressing movies.