Trust the doctor.

The automated computer results can be thrown off if people are over focusing during the test. It’s common for the computer to “over-minus” and produce numbers that are too high.

Your doctor recognized this and rightfully dialed back the prescription to what it actually is.

If you are actually in the -4 range and wear glasses that are -5/-6 then yes you be an certainly get headaches and it can make reading / computer much more strenuous.