What Causes Severe Fatigue While Having Sleep Apnea And Thyroid Disorder?

tired, like you have the flu but no fever, extremely fatigued, he is not an idle person and he keeps on keeping on but it is really getting bad,my husband has had these symptoms for a long time and we cant get an answer. He has had a cardiologist tell him he is ok no signs of a problem there. He does have sleep apnea and been on the cpap for 3 weeks and that has not changed anything, he also has thyroid problem and he is on the meds for that and the last blood work showed normal levels. Calcium level are normal, white blood count is normal. We just need an idea so we will know where to turn next.