Stop touching things..empty the tank at least halfway then start ob whatever cleanup your gonna do. A 24" tank should have cross braces and never heard of a rimless that big. Probably just need to get the frame for it again to repair which you could probably do with it halfway drained.. Either way don't touch your rocks/ coral/pictures anything till you get some water out!!! Very scary!
Sounds very serious and like a disaster waiting to happen. Can you take multiple measurements across the top to ensure its still at 24"? And if possible used something that is safe to measure the inner middle section, from back to front? Draining half the water sounds like the safest thing to do and should help you sleep tonight and avert any immediate disaster.
And yes, my wife will kill me if anything like this happens.
I would have a frame built for that tank, out of aluminum or something
Glass will not hold for ever, if you have pumps inside the tank the pressure that power heads can put on that tank will makes matters worst
Drain the tank
If you wanted to make emergency supports you an go get two hardwood planks and 3 or 4 portable carpenter vices make a temporary brace, you have to get the measurement right and still not fill to the top.
You can fix that tank you have to drain it first and have some epoxy brace rods from front to back of tank on the top of the tank which should have been there to begin with the glass is to thin and it needs brace rods to support that bow effect