looking for approaches to detecting outliers in individuals unequal sequential time series
Outlier detection doesn't sound like the most promising approach to me, as you have a model for the data.  Some ideas you could try: use a hypothesis test to check the hypothesis that the stress values fit iid Gaussian with pre-defined standard deviation and unknown mean; use linear regression to fit a line that predicts stress as a function of time, and see if the slope is greater than zero by a statistically significant amount; etc.