Is it normal to be obsessed with your sister?

Ok ever since my older sister visited from college this summer for her 19th birthday, I became attracted to her. She is very beautiful, her face, she has nice long black hair, nice body and she's sweet as a princess. She went back to out of state for college for her 2nd semester and I've missed her ever since. The only ways we keep in touch is through facebook and phone calling/texting. Lately I've been EXTREMELY obsessed with her! I get very excited when she replies to me and I have a slight crush on her. I won't physically do anything with her because she's my sister. I'm a girl btw im 18 and never found her this attractive in my life. She's honestly the most beautiful girl in my opinion, she looks a mix between selena gomez and demi lovato. Anyway I've been having very inappropriate dreams about her. Last night I dreamt that we were at a swimming pool and her boyfriend and her made out right in front of me. He sucked on her fingers then he spread her legs open and fucked her right in front of me! I've been horny all day long thinking about the dream. At the same time I feel guilty because of the dream and would never tell her because she would freak out. But anyway is it normal to be obsessed with your sister?