Loss of Muscle Coordination or Stiffness
Serotonin syndrome can cause your muscles to behave abnormally. This could be anything from loss of muscular coordination to developing rigid or stiff muscles. [8] For some people, serotonin syndrome causes them to lose some control over their muscles and they may experience involuntary symptoms such as twitching and muscle spasms. Myoclonus is the term for this intermittent jerking and twitching of the muscles.
In some people, the muscles become stiff and hard to use. Serotonin syndrome is not the only thing that causes the muscles to spasm or stiffen. If this is the only symptom you have, you should see a doctor. This is especially important if you have an open injury or cut. Tetanus can also cause this symptom, although tetanus symptoms are a lot more severe than those of serotonin syndrome.