No, just because you are healthy, that does not mean you don’t see a doctor.
What did your “regularly serviced” include?
Your transmission is about 140,000 miles OVERDUE for a fluid and filter change, not a flush. Your maintenance manual likely calls for that to be done at 60,000 miles or 6 years. It should be done by a capable transmission shop or the dealer. Avoid tire and muffler shops and Rapid Lube places!
I’m assuming the person who told you about the flush was not a proper transmission shop. If he was a good mechanic he would have recommended a fluid and filter change at 80,000 miles latest.
Transmission fluid typically is a pinkish red, totally clear when OK, and if you put a drop on a paper towel, it expands gradually to about the size of a silver dollar, with no deposits or discoloration anywhere.
At that mileage a FLUSH could indeed damage your transmission, since it will likely dislodge solid chunks of material that can plug the many passages in a transmission.
You are very lucky indeed that your transmission is still functioning!
Please read the rest of your owners manual with respect to other important items such as coolant change, oil changes, timing belt replacement, etc.