As people have said, it is life threatening and you do need to descend if feeling symtoms.
I have suffered from it 3 times, and each time descent is what has helped.
The contributing factors I have noticed FOR ME,
elevation over 10,500 feet, hiking uphill in excess of 1,000 feet, and limited time for acclimatization.
I have usually driven from 3500 feet elevation the night before, slept at 9,000-9,500 feet, then started hiking at daylight.
Symptoms have been mild to extreme, shortness of breath when at rest, extreme headache to the point of throwing up, lack of appetite, and fatigue have been most common.
My experience is if I descend back to 9k feet or less, by the next day I am over it and ready to go, but that 24 hours can be pure hell.
Woke up this morning at 11,500 feet with mild symptoms after climbing for 4.5 hours yesterday, by the time I descended to 9k feet I started feeling better, by the time I hit 7k feet I was good to go.
Once you've had it, you tend to pay better attention to what your body is trying to tell you at altitude, and you realize what you can work through, and what demands that you descend immediately.
Funny thing, 3 weeks ago I was above 11,000 feet mountain biking and never had any problems.