Hopefully you have not damaged the engine by driving it in the red area. It sounds like there might be a blockage or air in the system, assuming the thermostat is not stuck closed (they can be tested by heating in a pan of water on the stove with a thermometer).
Have you been flushing your cooling system every other year? At this point, do a complete flush with a heavy duty acidic radiator flush (buy at any auto store or even Walmart). Flush with your heater on and do repeated flushes, operating until after the thermostat opens and the water circulates, then drain, refill when cool, and flush again. Do it repeatedly until the water runs out clear. Then do one last flush - this one with distilled water. Look up your coolant capacity and refill with the correct red Toyota coolant to a concentration of 50% (so use 1 gal if your cooling system capacity is 8 qts, etc). With the radiator cap off, you should be able to squeeze the hoses and see the coolant level respond. That's a way to bleed off air in cars without an air bleed valve.
Do not allow the engine to run in the red. Check your oil for signs of milkiness that would indicate coolant in the oil. You can have your mechanic perform a cooling system pressure test to find out what's wrong.
Also, be careful double posting questions on Edmunds. I responded to this question last night but it disappeared when Edmunds deleted the double posting of the question just as I entered an answer. Keep all answers in this original thread by using the answer this question button below.