system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes that feeling of "emptiness" when someone experiences an episode of depression or sadness?
gpt
It is not fully understood by science but much research points towards some form of serotonin deficiency, in either its production or turnover in our bodies. Serotonin is a neurotransmitter that we synthesise from the tryptophan we eat in our food and helps us regulate mood. Whilst poor diet can clearly contribute it is also clear that certain experienced events can also disturb our brain chemistry. Generally speaking that emptiness will also coincide with a lower level of serotonin or an ineffectiveness of the serotonin receptors in our brain to process it.