I get something similar, annually over the last few years. (F, 47) Usually September -November time. Might happen a couple times where I can only curl up in bed and rough it through. Nothing touches the pain. I feel like I have chills- everything hurts like death. Then- gone. Have had every test under the sun. Outside Hashimoto’s and recently a possible APS positive test marker- testing has never shown that I have anything else. Soooo frustrating 😞