People diagnosed with serious mental illness -- schizophrenia, bipolar disorder, or severe depression -- die 20 years early, on average, because of a combination of lousy medical care, smoking, lack of exercise, complications of medication, suicide, and accidents. The U.S. has become probably the worst place in the developed world to be mentally ill.
Before taking the leap into retirement, we need to give a lot of thought to how prepared we are for 20 or more years without a paycheck. The most important question, of course, involves income and expenditures, those we can anticipate and those that are harder to predict, such as long-term care. And will there be enough left over to pay for some of the fun things we have been looking forward to?
Zombies are, insofar as I understand their biological classification, undead. They aren't entirely dead, but they certainly aren't fully alive either. That sounds a lot like life with a serious chronic disease. When one's life no longer involves pleasure or the pursuit of interests, it is something of a half-life.