The serotonin from carcinoid doesn't hit the blood stream, until it metastisizes to the liver. So you could have it for years and not know, therefore. All that serotonin pours into your blood and affects your heart and GI tract among other things.

Once it gets into the blood stream, it can dump serotonin when under stress, physical bending, activity etc. In some people it is easy to spot, others continue with vague weird symptoms that doctors cannot put together.

Since you KNOW serotonin is a problem for you... look to carcinoid or a hidden tumor secreting biogenic amines...lung/ovary etc.