Minivan Malfunction

Today my Mom’s minivan…a '98(?) Olds Shilouette…had something odd happen to the rear axle. The shock absorbers have for some reason extended all the way, lifting the van’s rear end abnormally high off the ground. Also, the rear end is so stiff that any bump in the road actually makes the rear tires bounce off the ground (or so it sounds and feels like;) ).

What caused this to happen, and how can I re-adjust the suspension to normal?

I have no idea what the problem might be but I just did a Google search using “olds silhouette shocks” and this site is first on the list: