I'm not saying your situation is the same, but we have had cracks appearing in the house over the 25 years we have been here.
I was paranoid there was movement in the house and had a couple of surveyors look at them over the years. I was told things were OK. However, over the last few years,small cracks have appeared in the side wall, along with a crack in the ceiling of the front bedroom that ripped the wallpaper covering it. We had another surveyor over who diagnosed very slow movement in the roof structure and recommended some additional bracing timbers in the roof to stop it spreading.
Have you got cracking appearing anywhere else in the building?