Looking at Webster's Medical Dictionary on Fatigue:
1: weariness or exhaustion from labor, exertion, or stress
2: the temporary loss of power to respond induced in a sensory receptor or motor end organ by continued stimulation
So that is not the professional meaning. The professional isn't bothered with 1 - they assume that the patient is likely to recognise it as normal and not consult a doctor about it.
OR they assume the patient is not self-aware enough to tell the difference, or the patient is catastrophizing because they read an article in Psych today.
So fatigue is used to mean weariness or exhaustion (or whatever) out of proportion to normal causes. So rheumatoid and lupus include fatigue as a major symptom.
So do depression and grief and ennui and eating too much turkey and laughing too hard, that is, cause weariness out of proportion.
And if fatigue is meant to be in lieu of exhaustion, I'd suggest changing to exhaustion because degree matters. Degree matters. Intensity matters. Levels matter. Medicine gets that as long as it's something objective and overt and mechanically measurable (although they still even get that wrong).
But it often seems to forget degrees - or is indifferent to them - when it comes to subjective symptoms. They'd generally rather err on the side of understatement, frequently at patients' expense, and call that understatement caution or prudence or whatever.
What ever happened to striving for accuracy in medicine, broadly speaking?
I'm not directing this little rant at you,
@Jonathan Edwards. I'm just yelling at the greater medical community.
It is what it is, this artifact of distrust and condescension, and not easy for the medical community to overcome, especially with the friction that would ensue.