Ceiling cracks- advice needed

We are due to have a new bathroom fitted from tomorrow. We live in a 3 story 70's townhouse, and on the top floor, we have the bathroom, and second bedroom. The pervious owners had put 2 and 3 layers of tiles in the wall. Because the bathroom is so small to start with, we decided to remove the tales, and have the walls parts re-plastered, part re-tilled.
We've spent the last few weekends removing tiles from the bathroom (all the walls are tiled). Today, we noticed that there are now hairline cracks, radiating from over the bath. There are two cracks, at right angles, and have moved from the bathroom, and across the ceiling of the whole top floor- into the landing and bedroom. Should we be really worried, or could this just be caused by the vibrations of having to chip off all of these sets of tiles?
Any advice would be appreciate, hoping that there is nothing seriously wrong! Toast.
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