Three elderly ladies are discussing their mental health. The first lady says, "Today I was at the top of the stairs, and I couldn't remember if I had just gone up or was about to go down."
The second lady says, "I was sitting at the edge of my bed and I couldn't remember if I was about to sleep or just woke up."
The final lady says, "My memory is as good as ever, knock on wood." With this she hits the table twice. Suddenly she is startled and looks up, "Who's there?"