This fits my experience with depression, and signs of my recovery as well....
Mathematically, it turns out, the shift from a healthy state to a depressed state resembles other so-called tipping points—moments of critical mass where a system, such as changes to Earth’s climate or a social trend—shift rapidly from one state to another. Theories on tipping points suggest that as a system nears a tipping point, it becomes less resilient.
“In any system, if you push the system a little bit out of equilibrium, then the closer it is to the tipping point, the longer it takes to return to equilibrium after that perturbation,” explains Ingrid van de Leemput, an ecologist at Wageningen University and Research Centre in the Netherlands who led the new work. Indeed, the longer a patient took to recover from feelings of sadness and anxiety, the more likely they were to be more depressed by the end of the study, suggesting that they were closer to a tipping point between health and depression, her team reports online today in the Proceedings of the National Academy of Sciences. The results matched with a mathematical model that the researchers had previously created to represent how emotional swings could signal an impending tipping point.