Once upon a time there was an artist/engineer who made a system he called the Narsci-system, after Narcissus, the greek legend of a man in love with himself, and system, as it was made of multiple sensors that communicated with a single point for concatenation and analysis. Also, because it was "Narcissistic" to pay so much attention to the goings on of his own body.
So I'm imagining a medical version of this. It would continuously scan and record the goings on of the user's body, and communicate back to a sophisticated computer for analysis. The computer, using the best advice medical doctors could give, would give advice about certain situations. If one hadn't gone to bed for 20 hours straight, it would suggest doing so. It would suggest morning jogs, and even tell you to speed up or slow down. (There is an ideal heart rate to achieve in aerobic exercise.) It would complain if you moved too little, as measured by the accelerometer, as this suggests laziness, or a lack of exercise, or too much, as this suggests the need for a day off. If it found a problem it didn't know about, it would suggest a medical checkup.
And in extreme situations, maybe it could even actively intervene. Heart rate dangerously low? Stimulant injection! EEG showing abnormality? Cortical stimulation! Dangerous level of vibration? Deploy airbag!