I suspect the ceiling was nailed to the joists as opposed to being screwed. Whoever hung the ceiling may has used nails of insufficient length allowing it to slowly pull away over time, crack and fall. Consider yourself fortunate you were not under it at the time because plaster/drywall by volume weigh about the same as concrete.
If you sustained damage to your property, review your lease to see if it addresses liability issues of this nature. Basically, in the absence of the lease having language to the contrary or local statute, to recover for damages you would have to show negligence on the part of the landlord. In other words, what did the landlord do or fail to do that contributed to or caused the ceiling to fall.