system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How do low serotonin levels affect the rest of the body?

Asking due to personal reasons. 
Also wondering if those levels can ever recover naturally.
gpt
Serotonin is synthesised naturally in the gut and the brain. Tryptophan is the amino acid used as the fundamental building block for serotonin but it's not as simple as consuming more Tryptophan to synthesise more serotonin due to something called the blood brain barrier. There are many serotonin receptors throughout the body that are classed in the 5-HT family with many subunits of th 5-HT receptor. As well as playing a vital role in mood they also play roles in blood pressure, heart rate, appetite, nausea, memory, sleep and many more. If you are worried about your serotonin levels you should speak to your doctor. There is also a condition called "serotonin syndrome" which is caused by an excess of serotonin but also has very negative side effects.