Psychic and d�j� vu.......?

Umm as silly as you may find me... I think i have these weird moments when ive felt ive been there and done that event before. It freaks me out. Also ive had a few psychic moments too like i had this weird dream and it came true. My nan (mums mum) said that her family has this alot though. My nans brother when he was younger had a nightmare that a looter/robber/thug broke into their school and stabbed the teacher about 16 times it gave me chills. He told his parents about his dream when it came true they were shocked. My mum had a dream when she was younger that someone stole stuff from my grandads video shop and it was smashed up. You do have to believe me and my family does tell me the truth. I just feel weird when these occur. Why do they occur? Does this happen to you at all? Thankyou for all nice polite answers, they will be appreciated! :D