My experience is very short, but very real.
I should say that I was very close to my dad's parents. I spent a lot of time with them growing up. They lived close by, and I'd spend after school time at their house. My grandad and I were close, I loved spending time with him.
After high school, I moved in with my granma. I wanted out of the small town I was living in, and she needed help with my grandad who was bed ridden. He and I shared the downstairs, him in the den, and me in his old room. Eventually he was moved to a home where he had around the clock care.
At the time, I worked 3rd shift except on the weekends. Shortly after his passing, I was woken up and he was at the foot of my bed. He was just looking at me, and we held eye contact for a what felt like a long time. He faded out, and I did not have any other visits after that.
On my honeymoon, my wife and I rented a cabin. Only her mom knew the phone number to the cabin. On the second day of the honeymoon, early in the morning, some voice said to me "Your granma has passed away". At 7:00 in the morning the phone rang. I jumped out of bed and ran downstairs. When I answered, it was my mother-in-law. She did not say hello or this is B, she said as I had already heard "Your granma has passed away". My granma had passed at about 4 in the morning, when I had heard the voice.
I've had all of my aunts and my mom tell me, that after I moved out of her house and moved in my girlfriend, she was very upset. Everyone has told me that they think she waited to see us married before passing.