Just one square metre can weigh up tp 40kg. This weight falling can easily kill a person or cause serious injury.
Inspect your ceiling to see if there are any signs of major cracking or sagging. You should get a professional plasterer to inspect suspicous ceilings.
Our company was called to inspect a lath plaster ceiling in a child minding centre which during our inspection totally collapsed. Fortunately it was during after hours and there were no children present.