And you have 15 seconds to get that oxygen mask on your face
At 36,000ft, the air is freezing. Like, -80F freezing. But don’t worry, you’ll only feel the frostbite for about 15 seconds before passing out from hypoxia, assuming you didn't get your oxygen mask on. Also, anyone who ignored the "fasten seatbelt" sign will, just like in the movies, get sucked out of the plane in seconds.
Pilots will try and get to a safe 10,000ft ASAP
Gradual depressurization is just as bad, as oxygen masks only have enough oxygen for a limited amount of time. Once that runs out, passengers become sluggish and fall unconscious. Before that happens, though, the pilots -- wearing more advanced rubber oxygen masks -- will try to bring the plane to a safe and breathable altitude of 10,000ft.