This was rather sudden, yes.
The day after I took Hera to the vet about the lump, I noticed two more, very small, lumps on her other side. They were all growing very quickly. By this morning she'd lost the use of her rear legs and her breathing was rapidly worsening. She didn't seem to be distressed yet, except at the very worst few seconds of breathing here and there, but neither was she having a lot of fun. We probably would have held off a few more days if it hadn't been for Aphrodite; they've been very close recently and I don't think there'd have been much positive left in Hera's life without her.
This weekend Aphrodite fell apart. She started bleeding from her genital area. She smelled terrible. She hid in a box and didn't want to come out (this, actually, had been going on a bit longer, and we feel terrible that we didn't notice anything was wrong sooner, because there were definitely behavioral signs). She also, as we found out when we got her to the vet, had a lump in her throat and a horribly swollen tongue, which was interfering with her drinking so she was dehydrated. The blood was in her urine; she also had a raging vaginal infection which started leaking pus.
So she got some injected fluids, along with antibiotics and a massive dosage of anti-inflammatory to try to bring the swelling in her tongue down to the point where she could eat and drink.
This did not work. She did stop bleeding, but her tongue only got worse; by Tuesday it was protruding from her mouth. Shortly after her nightly dose of anti-inflammatory and so forth, she either bit it or cut it on the water bottle and bled quite a lot. That didn't help the swelling any either (I had kind of been hoping it was an abscess and the cut would drain it).
So she didn't need to go through any more of that.