Leak from upsatirs bathroom ceiling is crumbling down help?

hie a few weeks ago i noticed a leak coming from the bathtub and since its been frequent even if tub is not filled up.just a few minutes ago was watching telly and heard a noise as if someone if pelting my door with pebbles i went to check only to fin bits crumbling of the ceiling then a sudden wooosh the ceiling plaster fell off just missing me.do you think my tub is going to fall down please help im alone at home and dont know what to do....