Similar boat but for me it was narcolepsy. Still working on getting the right prescription but it was definitely a feeling I could describe as "relief" to hear that there was a specific physiological cause my constant fatigue. And that sense of overpowering weakness that I was thinking of as being "really, really tired" was actually cataplexy. Just putting a name on it feels like a weight being lifted. Although I'll actually feel better when I land on a practical treatment.