I decided not to wait for my friend to help me fix my bed on Monday. The mattress was listing to the right and the rails were bending. Putting my weight, primarily in the right side every night, was not helping. I was afraid the rails would break.
So... I took off the mattress, dust ruffle, and box springs. It was worse than I thought - instead of just the clamp in the middle simply being off, the struts - both of them, had sheered away from the rail, not simply losing the rivet, but actually breaking off. Now, before you say something about the nearly 300-lb woman breaking her bed, I will point out that I bought this bedroom set in 1987 at Sears, and it is made of pressboard, not solid wood, so the fact that it has lasted - especially with my weight - for nearly 30 years without mishap is amazing.
There was an empty plastic underbed storage box there, and it's pretty sturdy. I put it under the broken struts, put the one clamp back on the one, and then put everything back, turning the mattress as I went. I think it will hold. So it's not listing anymore. I went and got a cold glass of milk, then laid down to 1) test it out and 2) let my back rest after all that. In a little while I'll get up and get my laundry together for tomorrow and my trash and recyclables together and out, and then I'll work on the kitchen and bath. But for now I'll stretch out and enjoy a completely horizontal mattress. I go get A from work at 1 am.