That's what mine did. Hit me on the head while I was loading something. Its your struts. They are not able to hold the weight of the hatch after it opens. Mine would open fully then gradually drop back to about 3/4 to 1/2 open.
I am sorry you are experiencing concerns on your Cadillac SRX. I understand how frustrating it can be to have problems with your rear deck, especially if the concern could cause an injury. I understand you are looking for advice from the forum, but if you would like to send us a private message with your VIN I can look to see if there are any service announcements or recalls open on your vehicle.