Can you show some photos of the sinking shelf? When I picture a super susan, and think about the shelf falling, it's basically the entire cabinet failing. I'm guessing your situation might be different than what I'm picturing.

if you're describing a fixed shelf in a corner cabinet, where a lazy susan mechanisms is mounted on top of that fixed shelf, then I would suggest adding solid wood cleats to the sides and back of the cabinet to support that shelf. If this doesn't sound like your situation, post a photo. (Note that adding the cleats permanently fixes the height of that shelf, as it should be, so you could raise it a bit if you want more height on the lower susan.)

Also, you can add (or hire someone to add) a vertical, diagonal filler at the rear of the susans so that things can't fall off back there.

Having just moved in, I'm missing some things--including the cord that moves photos from camera to laptop. So no photos of my own, but here's one from the web.

A vertical metal pole runs down the center of both shelves. The top shelf slid down it to touch the tops of the stuff on the bottom shelf. A bottle of vinegar toppled over the very short rail that edges the lower shelf and landed in the far back corner of the cupboard.

I guess I can just ask a handyman to fix it, since i can't kneel and thus can't look at the underside of that upper shelf.

I'm merely curious about what's meant to keep the top shelf from sliding down the pole, why it didn't work properly, and if this is a common problem--one that might keep recurring even after an initial "fix."

Super Susan #2 is OK thus far...

Ok - if you have a pole, it's probably a lazy susan and not a super susan - the photo doesn't show a pole and instead shows the "fixed shelf" configuration I mentioned.

In your cabinets, do you have that piece of wood/MDF that is shown in this photo? Or just the trays that your bottles sit on?

You dont have a super susan. You have a regular lazy susan. The difference is mainly the pole in the middle. Super susans dont have that, the upper shelf sits on a permanently installed fixed shelf. You can see this in the picture you posted.

What keeps your upper shelf from dropping is likely a set screw below the shelf. It probably needs to be tightened

What you're describing versus what is pictured are not the same. The picture you posted is a Super Susan, it has a full fixed shelf to support the turning portion and has no need for a pole. What you've described sounds like a regular lazy susan, not a super susan. Depending on the manufacturer, there is a probably a bracket and a set screw holding the bracket in place that was not tightened down (or is not strong enough to hold the weight of the items on the top shelf). Given your physical limitations, a handyman or woman (or neighbor?) may be your best bet, because you have to get underneath the shelf to adjust it.

Or maybe install a different unit that pulls out - Rev-A-Shelf makes a number of different styles and options.

There are other solutions for corner cabinets. Here's a gallery.
(given your "I have trouble bending over" issues, the drawers might be really useful! If you can't do new drawer fronts, you could have pullouts made to go behind the door--one of these says they can't be added after-the-fact, but I have some skepticism about that. You might lose some storage width to a wooden framework that you fasten the slides to, but it can't be impossible)

https://www.thekitchn.com/8-ingenious-ideas-for-corner-cabinets-organizing-ideas-220071#gallery/49672/1

This guy installed corner cabinets when the cabinets were made, but it shows you how much space you'd get. And it shows the supporting vertical members (those are pocket holes holding the vertical supports in place)
https://www.youtube.com/watch?v=4Mj1bjSBbSk


THIS GUY retrofitted pullout drawers in his corner cabinets. At the beginning, you see him remove the Super Susan shelves and the curved back of the cabinet. And at 10:43, you see the freestanding frame/unit he made to hold the new pullout shelves (and presumably fastened that frame to the floor of the cabinet)
https://www.youtube.com/watch?v=cv59XNLlBVE

There should be a screw somewhere that holds that shelf in place--maybe it goes through a section of the shelf itself, or maybe it's on some sort of collar below the shelf.

That screw may need tightening, or it might have lost its thread. If tightening it up doesn't work, someone who was jury-rigging might get a pipe clamp to tighten around the center pipe, and if necessary, take a flat piece of wood and drill a snug hole in the center of it so that the wood is resting on that pipe clamp.

Many thanks to all who have replied. I now know enough to feel confident discussing this with a handyman and hiring one to fix the thing--and if that doesn't work (or it doesn't stay fixed) I have some alternatives to try.

No more responses are necessary, and I'm extremely grateful!

My daughter has such an arrangement in her corner cabinet.

I am mixed in feeling about it. On the one had, it has an easy factor. On the other hand, there is a limit to the types of things that you can put on it and still expect it to function.

If the pots and pans are not just exactly placed, it will not turn.

Since it is down under and you have to get down there to fuss with it, I find it to not always be a good solution.