What is it like to have a strong "altitude sickness"?

Altitude sickness will make your heart beat faster, you will have difficulty breathing, and your whole body will collapse. The feeling is very uncomfortable.

I felt this feeling when I was on a business trip in Tibet. I didn’t feel anything strange when I got off the plane. But when I went up the stairs, I only walked a few dozen steps and I felt it. I felt out of breath, and then I returned to the dormitory after resting for a while.

Because I was running all the way, I wanted to take a shower and rest as soon as possible, but because I used too much force when taking a shower, my heartbeat accelerated and I had no strength at all. If my colleagues hadn’t helped me back to the house, I would probably have died. I had to pass out in the bathroom.