Like general system theory, Non Linear Dynamics (NLD) starts from equilibrium, cybernetic principles of feedback and feedforward, self-regulation and deregulation. However, NLD equilibrium is considered to be dynamic. Only when fluctuations become too heavy or too frequent do instabilities occur. Then, the system may jump to a new equilibrium. Feedback mechanisms are assumed to contain not only circular but also non-linear causality: small differences in initial conditions may cause big differences in the end (or none at all) and the predictability of such outcomes is limited as well. Both insights apply similarly to the regulation loops..
Using NLD, one can explain transitions of quantitative into qualitative changes and develop indicators to predict those order transitions. NLD is therefore eminently suited to conceptualise the bio-psycho-social mechanisms underlying health and disease. In particular the transitions from acute into sub-chronic and from sub-chronic into chronic complaints can be modelled as a departure from the (health) equilibrium, indicated by processes that show a strong increase or decrease in variability and complexity.
To study the dynamics of the biological, psychical and social systems one may use computer simulation because computers can compute and visualize non-linear relationships even though these cannot be solved analytically