Do I have some sort of paranormal activity?

I don't wanna believe in ghosts, nor do I want to ever encounter one, but I may have had a paranormal event happen the other night. Well my room is in the basement, which has pretty nice suite, nd I was sleeping on the couch watching t.v, when all of a sudden the doorknob (which I had locked, thank god) started to shake as if someone was trying to get in. I asked who it was, and it was so clear I heard "It's me", it sounded like my mother. I got up and opened the door to find noone there at all... my mother was in a bad accident, so there's noway she could've hidden anywhere in time. This event is so subtle that it doesn't make me a strong believer, but still it happened. I always feel like there are eyes watching me, nd my cat who is dead now would always stare into the laundry room forever. I'd have friends over nd they would say they would hear footsteps on the stairs, nd my one friend said she was being suffocated (i don't believe her). I never would tell my friends that I thought the place was a lil haunted, they'd always tell me before. It's odd, but what could explain this?