The following sequence-internal condition --> symptom perception --> appraisal --> decision-models various symptom-based self-regulation processes. A formal mathematical model describes the first three steps by continuous variables and the decisions at the fourth step by binary variables. The stochastic transitions between the sequential steps are quantified by transition probabilities. The model is illustrated by blood glucose level estimation and detection and treatment of hypoglycemia in 78 patients with insulin-dependent diabetes mellitus. These patients made 50 to 70 data collection trials over 3 to 4 weeks recording perceived symptoms, cognitive-motor performance, subjective estimates of blood glucose, decisions about treatment of hypoglycemia, and driving. A statistical estimation of the model's parameters demonstrates the utility of this approach for understanding the awareness, detection, and treatment of hypoglycemia as a process of symptom-based decision making.