In house water pressure goes down to almost nothing-good pressure at the well head of 40/60 always. Entire system is 20 years old. Pressure tank is suspected culprit or the switch may be worn bad enough to be an issue. Could the pressure tank bladder being bad cause this issue?

If your pressure gauge is reading a steady 40 to 60, and pressure holds in that range, then your switch, tank, and pump are doing their jobs. A few questions:

When pressure drops to nothing in the house, does your pressure gauge still read 40 to 60?

Do you have a filter/softener on your system?

When you are not using water, does pressure hold steady?

One thing to try. There is a little air valve on top of the tank. Depress the valve stem for three or four seconds. If you get nothing but air, then good. If water comes out, then the tank is bad.