I wonder if the accelerometer in a smartwatch could measure levels of pain in a patient? I wonder if tense muscles and other aspects of suffering could be measured and tracked.

I suppose a smartphone app could ask the patient to tap one of the ten pain-level smiley - frowny - sweaty faces at intervals as well.

If so, there'd be a way to measure how fast these painkillers clear from each patient. It might even make it possible for some patients safely to play an active role in their own dosing. Avoiding wide swings in blood concentration is the safest way to go.