As a passenger, surely there was some indication of loss of pressure (noise etc?)
Very often no indication of depressurisation in the cabin, you are not in a hollywood film!
You will only get it if you have a structural failure (door, window, floor...) as in this case you would have an explosive decompression with vapour and air sucked outside.
For the Ryanair airplane as they did not find any obvious reason for the depressurisation it is probably a failure of the air conditioning system giving a relatively slow depressurisation.
As for the plunge to the earth, it is nothing as dramatic as people imagine and I am pretty sure some can continue to sleep if nobody take care of them.
But I agree, passengers and even some cabin crew are frighten and need a good PA to comfort them.