Whilst ceiling collapses are not exactly common, they can be a problem in homes built more than 30 years ago. There are also potential issues with homes built more recently.
If your home is over 30 years old there is a chance that your ceiling may be made of a material called plasterglass, which is suspended rather than fixed in place. This was a common building practice, where the ceiling is supported by straps that are laid over the timber ceiling joists and grouted into position. Over time thermal movement in the roof space causes the timbers to expand and contract, which causes the strands within the plaster straps to break. This can cause the ceiling to sag or even fall.