DifferentialEquations: Gaussian error term in one of the equations makes it extremely slow (and error prone)

[ChrisRackauckas]

@MvanSteenbergen

Thirdly, the rate of the noise ζ(t) is chosen at 0.01, meaning that the perceived environment variable z changes every 0.01 days (noise will be generated every 14.4 min). It is a compromise between the duration of variability of the symptoms of psychiatric disorders and their environment (i.e., considering a psychological state change every 14.4 min). In other words, the model provides a smoothness of 14.4 min, i.e., informs about potential changes in its variables approximately every quarter of an hour.

You should implement this as a discrete callback which changes a parameter according this this schedule. I recommend using a PeriodicCallback.