i've chronic fatigue
it's pretty tough to determine unfortunately. and if you do have it you'll probably have to put in more work around determining that fact than doctors will care to do for you.
there are nigh endless reasons you could feel tired. it's kind of like headaches in that way; could come from practically anything. difficult to diagnose without a lot of time, effort, and trial and error because of that.
some other terms that apply to me specifically are dysautonomia and POTS (Postural Orthostatic Tachycardia Syndrome). i've been nearly, though not entirely, bedridden for the past 20 months since onset, with temperature dysregulation, heat sensitivity, constant tiredness unrelated to sleep type and amount, brain fog, and bloodpooling. the severity of my symptoms vary on a monthly, weekly, and even daily basis based on energy expenditure and what seems to amount to chance.
sitting upright, standing upright, and especially standing still will without fail gradually increase my symptoms. after 30 minutes i can't sit anymore, and after 10 minutes of standing completely still with my back flat against a surface my limbs will be utterly purple, i'll be itchy all over, i'll be wildly short of breath, i'll be dysfunctional for the rest of the day and likely the next few days thereafter.
all that is merely my own experience. i do not a great deal of others' experiences with chronic fatigue, nor do i know much of CFS in particular. that's partly, though not wholly, because it can encompass a great many things. your symptoms need not be the same as mine, nor nearly as severe i imagine. i also imagine there are those whose symptoms are even worse than mine.
one thing of note with chronic fatigue is that if you have it, as i understand it, exercise will make you feel worse, not better. which is quite the pickle. because exercise is good for your health in a lot of ways. but with CFS pushing past your energy envelope tends almost invariably to make you feel worse, and noticeably so, in the days that follow, not better. and the more often you push past that energy envelope the worse you'll feel and for longer.
if you're not sure whether you have it, it's difficult to determine whether you do. all i can truly suggest is listen to your body. experiment with energy expenditure as you see fit, but cautiously and only when safe. test your limits sometimes and if you feel it right to do so, not all the time. even if rest won't make you feel all better there's no sense ignoring the need for rest and feeling worse. the important thing is to stay alive and live as fulfilling a life as you can under the conditions you have in the moment.
