Your hot end does not need to stay exactly at the target temperature during printing. It is completely normal for the temperature to fluctuate above and below the target within a few degrees during printing and there is not a problem.
For older PEEK style hot ends, if your hot end falls to 180C or below during printing, there is a good chance that one of your heating resistors have failed and needs to be replaced. They may have simply come to the end of their life and will need to be replaced. You can check the heating resistors with a multimeter if you would like to confirm the diagnosis. To do this you will be checking the resistance of the heating resistors. With the printer powered off completely, you will use a multimeter by contacting the probes against the crimps that are on each side of the heating resistors (just above the nozzle on the hot end) 1 for the positive side and 1 for the negative (polarity does not matter) When checking the resistance you should see a reading of 3.8-4 ohms for good resistors and anything greater than 4ohms is an indication that one of them is in fault and needs to be replaced.
You can find a video that we created showing how to change the resistors here: Changing Resistors
Alternatively you could upgrade to our most current hot end the HE280. It would require two items: