Wheel Bolts problems of the 2005 Toyota Prius

While driving my 2005 Toyota Prius, the rear passenger wheel became so loose it was causing the car to vibrate and shake. I thought it was a flat tire, pulled off of the freeway I was driving on onto the shoulder. There was no flat, pulled off at the next exit into a garage. My husband, whom I called by cell, told me that it was a loose wheel probably. The garage mechanic raised the car in the air and the wheel was ready to fall off. He checked over the wheel, etc, re-tightened the wheel, and found that all of the wheels were loose, but none this badly. The last time the wheels were off was in April and had not been checked after that for tightness. As I looked in the owners manual it says to check them every 1000 miles or so. This is a very dangerous situation. This information should be in bold print and pointed out to every new owner the importance of checking the tightness, if this is a consistent problem. I was lucky! it scared me a lot and I am nervous when driving the car now. If this is a common problem, it needs to be addressed with emphasis!.