What happens when an aircraft has pressurization issues?

A recent Delta Air Lines flight from Salt Lake City International Airport on its way to Portland turned around and landed back in Salt Lake shortly after taking off because of pressurization issues, per KSL.com.
Soon after the flight took off, passengers reported hearing strange noises and feeling the plane dipping.
One passenger said their ears started to pop and then they noticed the plane was circling above the Great Salt Lake.
Passengers were not told what was going on.
According to KSL.com, Delta Air Lines said the plane was unable to pressurize above 10,000 feet.
Once the plane landed back in Salt Lake City, some passengers were met by paramedics. Ten passengers needed medical attention and Delta Air Lines covered transportation for those passengers to medical facilities, per KSL.com.
Passengers on the plane sustained injuries such as bloody noses and busted eardrums from the pressurization issues.
“The cabins of modern passenger aircraft are pressurized in order to create an environment which is physiologically suitable for humans,” per Skybrary.
According to CNN Travel, as altitude increases the air becomes less dense and with fewer oxygen molecules, breathing becomes more difficult. The effects of this can be felt over 10,000 feet.
Most aircraft pressurize to what air would be like at an altitude of 8,000 feet, a pressure that is safe and comfortable for humans.
According to The Washington Post, there are a variety of reasons why an aircraft might experience depressurization “including structural malfunctions to windows, doors or sealed pressure vessels, as well as incorrectly activating the cabin’s pressurization controls or structural malfunctions to the aircraft’s overall system.”
One of the biggest medical concerns when a plane loses pressure is hypoxia “where lower levels of oxygen prevents a human’s organs from fully functioning”, per The Washington Post.
Hypoxia can occur in minutes, the first symptoms occur in the brain, manifesting as loss of judgment or confusion.
Other symptoms include increased breathing rate, lightheadedness, dizziness and poor coordination. Those experiencing hypoxia may also feel euphoria.
Loss of pressure can also cause barotrauma, an injury in your sinuses or ears caused from pressure change, per CNN Travel. If there is gas in the stomach of a passenger that gas will expand and the stomach will swell up. Pressure changes can also cause a tooth filling with a hole in it to blow off.
According to CNN Travel, the first thing passengers can do to minimize risk when the cabin loses pressure is make sure they are wearing their seatbelt.
Sudden loss of cabin pressure can create suction which can eject people and items from the plane or throw them around the cabin. Wearing a seatbelt helps passengers stay safely in their seat.
Oxygen masks are also critical, especially when loss of pressure happens at high altitudes. Supplemental oxygen from the masks helps prevent hypoxia.
The first thing the crew of the aircraft will do is rapidly descend to below 12,000 feet, where aircraft occupants can breath without supplemental oxygen, per Aviation Week. Passengers are advised to listen to their cabin crew and follow instructions.