Employment and dialysis

I'm at a quandary with my current employer. Business is not good, and I have little faith in the current management, but at least my job provides me with health insurance. Right now, I've managed to stabilize my gfr at about 16, and I'm in good health (early 50's), but here's the problem; I work evenings, and the HR person has made it clear that I was hired specifically to cover that shift, and only that shift. I fear that, once I do start dialysis, I will be unable to work a full shift after treatments.

In the interim, another employment possibility has arisen, one which is a day-shift job, for about the same pay or slightly higher (and with a better possibility for overtime, as well). If it weren't for my kidney situation, I'd jump on this opportunity in a second. But, there are those things to consider. As of the present, I still don't have a functioning fistula, and I WAS planning on getting that done this spring. Also, the COBRA payments would cost me about $1000 total, before I would get picked-upon the new company's insurance, but I would recoup that amount in the first year just from higher salary.

I'm torn as to whether I should be completely forthcoming about my health situation, be only partially forthcoming about it, or to not discuss it at all, and let it be a surprise for them when my kidneys finally have failed. I can make a convincing argument for each scenario, so I guess I'm just wondering if anybody else has been in a similar situation, and how that worked out? If you kept it secret, did they hold it against you in the end? Or, if you were honest, did that work out, or did it ruin your chances?