I'm so sorry that after voluntarily leaving your 20-year career, you've found gainful employment so quickly. That does sound horrible. I can understand why you are so scared. It would have been much more comfortable to have been fired, and then unable to find new work because you're older than your competition. Unfortunately, you took the easy route of leaving your position, and then had the misfortune of waking up and finding a job offer in your inbox. I don't think I have the meddling experience to advise you. I suggest you visit a priest.
Scared for you,