A speech model constructed from reference speech samples, which were produced by a subject at a first time while a physiological state of the subject was known, is obtained. The model includes (i) acoustic states exhibited in the reference speech samples and associated with respective local distance functions, and (ii) allowed transitions between the acoustic states. A test speech sample that was produced by the subject at a second time, while the physiological state of the subject was unknown, is received. Test-sample feature vectors that quantify acoustic features of different respective portions of the test speech sample are computed. Based on the local distance functions and the allowed transitions, the test speech sample is mapped to a minimum-distance sequence of the acoustic states. In response thereto, an output indicating the physiological state of the subject at the second time is generated. Other embodiments are also described.