I did some research on serotonin. I found that some researchers conider serotonin as a stress hormon. Most complete information in Ray Peat works. You may also follow the references he was using. The bottom line: high level of serotonin is bad. The SSRI should be avoided.
The serotonin is produced in the gut so that upset stomach, bloating and other problems typical in AF increase serotonin production. The higher level of serotonin makes people more tired, moody etc. (check the SSRI side effects or prozac forums). On the other side higher level of serotonin upsets stomach (increase serotonin production. I am not sure if it forms a vicious circle). High serotonin kills sex drive, causes hair loss etc.
I added extra vit A so that daily intake about 20 000 IU. I have read somewhere that vit A reduces serotonin. I started to feel better in about a week. may be just coincidence.
Three weeks ago, i did blood tests free fatty acids, PTH, Prolactin, Lactic Acid, serotonin.
Serotonin 1912 nmol/L (170 - 1134 nmol/L)
The others were within the range (may be not optimal).