The casual passenger has no idea, especially if there isn't any warning. So, if one is sitting in 65k in relative serenity when all hell apparently breaks loose with masks appearing and the aircraft dropping like a proverbial brick with attendant noise and shudder, why in hell wouldn't he or she be terrified?
On the other hand you can be like the little old lady on her first flight Nauru to Apia, Samoa. A four hour flight normally. 30 years ago. 737-200. Dark night departure.
20 minutes out of Nauru 31,000 ft uncommanded de-pressurisation with cabin rising. Emergency descent started (rightly or wrongly as it turned out). Oxy masks didn't drop because cabin never got above 14,000 ft. Cabin was under control passing 25,000 ft and aircraft levelled out and decision made to go back to Nauru. Appropriate PA made to passengers and cabin attendants. All OK down the back except for a few sore ears.
Landed Nauru and passengers disembarked while techs fixed the pressurisation.
As the little old lady was helped down the stairs, she said quite serenely to the cabin attendant "That was a quick flight - Are we at Apia already?"
