https://www.s4me.info/threads/serotonin-reduction-in-post-ac...
There is a lot of crap science published, and that serotonin paper is pretty poor.
Anyway, it's up to you what science you want to pursue. I managed to recover from ME/CFS myself by looking deeply into the science, so I'd recommend looking further. Stress seems to be one of the major issues. Anyway, from what you say it sounds like your symptoms are pretty mild (correct me if I'm wrong here).