I've seen ghosts twice.
The first one was a generic floating monk figure with a pitch black face that appeared to me when I was 4 or 6. I was fully awake and walking around. I even spoke to it before it disappeared.
The second one was my dead grandmother when I was in my early 20s. I was cooking and she just stood there a few feet in front of me. I even closed and opened my eyes and turned around and back to see if she would disappear. She vanished when I started to walk towards her.
I am a skeptic and an atheist. I am also a little insane.