Heart disease fits the best. Your heart is dying, it can't pump blood properly. To compensate it tries to grow larger, it swells and you get a giant heart. At some point it collapses since the problem was that the heart was leaky or the arteries got clogged or the muscles has some issue etc, growing larger can compensate in the short term but eventually you die anyway.
So it is similar to how a government that tries to grab more power and become larger is a red flag for corruption or inefficiency. The problem isn't that it tries to grow, the problem is that it is corrupt and inefficient in the first place, the country is then dying no matter what.
Countries can be replaced however, and small governments are easier to replace than large ones, so ideally should fix the government before it grows too large and powerful to easily be replaced.
The country freezes in rigor mortis, and can no longer take actions.
Politics or governance often feels like its experience brain death.
You get bloat and deflating effects, bubbles that inflate and pop.
You get a lot of social events that humans would describe as "putrid".
You get flight or escape of those that can leave for a new host, others flee to the remaining healthy areas.
You have external "parasites" / enemies removing portions of the empire/nation.
The process usually results with breakup and collapse in prior body segments.