1. A method comprising, by one or more computing devices: accessing one or more data streams from a plurality of sensors, the sensors comprising an accelerometer and one or more of a heart-rate monitor, a blood-pressure monitor, a pulse oximeter, or a mood sensor, wherein: the data streams comprise accelerometer data of a person from the accelerometer and one or more of heart-rate data of the person from the heart rate monitor, blood-pressure data of the person from the blood-pressure monitor, pulse-oximetry data of the person from the pulse oximeter, and mood data of the person from the mood sensor; a first data set from the data streams was collected from the person at a first time, the person being engaged in a first activity at the first time; and a second data set from the data streams was collected from the person at a second time, the person being engaged in a second activity at the second time; analyzing the first data set and second data set with respect to each other; and determining a current stress index of the person based on the analysis of the first data set and second data set with respect to each other.