Bob's grandfather liked to tell stories

[Bassim]

I am wondering if my sentence is grammatically correct.

Bob's grandfather liked to tell stories from the Second World War, but he would soon lose the thread and drop off in his armchair.

 

[emsr2d2]

It's correct.

 

[Tdol]

How about nod off instead of drop off? The meaning's the same, but it has more of a visual element of him losing track and falling asleep to me.