It’s an unbelievable type of fatigue, not like any typical type of fatigue I’d ever felt. “Fatigue” really isn’t the right word, because it sounds like you’re just “tired”. But it’s much more than that, and different than that. I would say it’s a combination of fatigue and “weakness”, really going along with the “Muscle Weakness” category. I’ve heard it described as one’s “battery being unplugged”, which is a good description. It’s like there was just “nothing there”: I couldn’t move, or could hardly hold my head up at times. Towards the end of my “T3 only” trial, I was afraid I was experiencing an Addisonian or Myasthenic crisis; I felt so weak I could hardly get up the stairs. Within 24 hours of starting the T4, I felt much improved (taking T4 is one way to mitigate a “T3 toxicosis” but this cannot be used regularly for this purpose). When I was flaring, I learned to take a little bugleweed to help decrease the T3 level in an emergency situation and mitigate or end the symptoms.
As time went on, in the later years, I learned to distinguish this feeling of “fatigue” from the feeling of “weakness” more. It turned out that for me, “fatigue” occurred more with feelings of “hypo thyroidism”, while the “weakness” occurred more with “hyper thyroidism”. It took me a long time to feel the subtle differences between these two, but there were differences. The weakness was more like I wanted my muscles to respond, but they couldn’t – it was like my tendons were “wet noodles” and my muscles were mush. With the fatigue, I was so slowed down systemically, that I simply couldn’t move at all and felt too fatigued to even try. From a quality of life issue, this difference doesn’t really matter, as both could basically render me non-functional. And since I was often experiencing both “hypo” and “hyper” symptoms at the same time, I essentially was often experiencing both of these together anyway.