This happened about 2 years a ago (I was about 13). I had just finished a book about this psychic who had a ghost come to her for help on passing on, the book was based on a true story. Well, since the book dealt with contacting the other side, I wanted to see if it worked.
I was bored so after finishing the book I started concentrating really hard trying to communicate with the other side. I was focusing on the name Aaron (which was the ghost's name in the book, though it had been changed to protect the people involved). And as I was focusing I felt a slap on my wrist. I got freaked (and it broke my concentration) so I immediately stopped and turned on the TV.
The next day I told my mom and she said that it was probably giving me a warning, that I was supposedly opening an unknown portal and whatever slapped me was warning me about that. She also said it could have been my guardian angel. I really don't think it was a ghost because our house is blessed, so it stops "evil spirits" or just spirits from entering, or so we believe.
Another incident that has happened 2 times in the past are knockings on my window. It's a one story house, but it still freaked me out, obviously. We have a dog, and when those incidents happened he didn't bark and it usually barks when someone he doesn't know is near, and it didn't so I'm not sure what it was.
Any ideas?