Is it possible a facet syndrome comes from doing a mckenzie excersie for the first time after gaining a lot of weight and not excersing for two years?

See your doctor: It is quite possible. However facet syndrome is usually a slow progression with facet hypertrophy and often thought to be chronic in nature. The extension exercises are more likely to make the chronic condition more symptomatic. There are exercise regimens and spinal injections that can help keep the symptoms controlled. Best wishes.