This really stinks, Catch. I've been there.

I realized I was not capable of doing my job long before my boss was. I was a payroll clerk/secretary/clerical everything for a utility company.
Does your firm offer long-term disability? You should check out your options in case you have to retire. Can you work part-time somewhere?
In my case I knew couldn't work anywhere anymore. I just felt like I was not reliable at all. I always worked above an beyond the call of duty, it.'s just my nature. I really don't know what I would've done if I didn't have long-term disability. I do miss working a lot though.
Good luck

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