Medical insurance.

In my experience, if you are over 65 YOA your options are extremely expensive.

I waited far too long to retire.

If you are only 3-9 months in Vietnam, a travel insurance (which you apply before you leave for Vietnam) is probably the cheapest option. There are certainly some travel insurance providers in Spain.

If you are staying in Vietnam for a longer period of time, you can opt for health insurance. But they are very expensive (200-500$/month).  For this money you can go to the hospital or to the doctor many times in Vietnam.
Some here in the forum have recommended BaoViet health insurance.
This is much cheaper than e.g. Cigna.

Thanks, I think I'll take a health insurance before travelling.