If you have been digging around your house, if there is a large tree or trees adjacent that are still there or have recently been removed, if you have a water main or drainage leak, if you have put a heavy load upon your house or removed something structural, if the council or water, electric, telephone, gas, cable utilities have been digging near your house, if your house suffers from traffic or aircraft vibration, if something like Buncefield has happened near you, if you have removed or installed a concrete path or impervious apron of some sort near your house, or if you and your neighbours either side, at the rear or across the road have done something similar to all of the foregoing, then you probably have settlement or subsidence and should panic.
Otherwise just fill the cracks in with ordinary filler, keep an eye on them and hope for the best. It may be just that in this cold weather you have turned up the heating a bit and caused non-structural shrinkage.
But it would be wisest to sleep round at your mum's for the next six months.