Fibromyalgia is more than just a placeholder, there are specific symptoms associated with it (such as the presence of myalgia in multiple locations on both side

Fibromyalgia is more than just a placeholder, there are specific symptoms associated with it (such as the presence of myalgia in multiple locations on both sides of the body above and below the waist), it's just that it's severely understudied, not much is known about the cause, and it's pretty much diagnosed by exclusion. Fun fact, the drug Xywav which has been FDA-approved for narcolepsy (and ideopathic hypersomnia) has also been shown in studies to help with fibromyalgia. They even sought FDA approval for that but the FDA rejected it on the grounds that there are too many fibromyalgia patients and therefore the risk of abuse is too high (the drug is related to GHB).