If you think you are serotonin deficient, you could try taking some 5-HTP. It is the body's precursor to serotonin and melatonin. I take it as a replacement for an SSRI. I take 100 mgs every morning. I also take 200 mgs of L-Theanine and a 1000 mcg B-12 lozenge.

The 5-HTP resolves the looping mind issues I have otherwise. My mind would get stuck on meaningless and mundane thoughts. It could last for hours and even days. 5-HTP resolved that.