Dear YEN, I am not sure but maybe your father's sympton is the same as one of mine. Mine is benygn, occurrring only when I've been sitting for awhile. At the table Imay drop an eating utensil or if my eyes tire when reading, the book will drop to the floor almost always thereby awakenjng me. For me , the symptom is met by holding something in my hand. All the foregoing has merit only if we are in fact dealing with the same thing. I am 83, dxxd in 84. Good luck to you my friend. Sam Kalkstein aka Abakalk.