Why would Guaifenesin (Mucinex) improve energy, mental well-being, and empathy?

Taking Mucinex, my SO reports an increase in energy, a big drop in anxiety and depressive thoughts, and just generally caring more about life. There's very little research on Guaifenesin, and I wonder if anyone has some theories or has experienced anything similar. It has muscle relaxant and anticonvulsant properties.

https://en.wikipedia.org/wiki/Guaifenesin

Update: I should have added this is NOT Mucinex-D or DM. No other active ingredients besides 600mg of Guaifenesin. https://www.drugs.com/pro/images/dd379cdd-90ab-42e0-ad89-f50d3220f611/mucinex-01.jpg

More research: This is a well-sourced rundown on Guaifenesin in the context of fibromyalgia. http://web.mit.edu/london/www/guai.html