When you develop thyroiditis, your thyroid output slows down, making you go hypo to some degree(depends on how bad the infection is).
As the infection starts to clear, excess hormones are released along with dead tissue as the immune system cleans up the mess. That drives you hyper, to a degree determined by how much gunk is getting into your blood.
When the infection clears it scars the gland and the function is often reduced by a small degree.
There are other reasons a person can go from hypo to hyper, or te other way around, but thyroiditis is very common if you have hashimoto's.
It could also be;
A shift in the dominant antibody.
A change in body chemistry like pregnancy or menopause or severe illness.
Over medication or under medication.
Certain drugs affect the thyroid.
Excessive iodine ingestion can cause problems.
I don't know if this helps but my doc told me that as your thyroid starts down the path to either hypo or hyper it is common to go back and forth to extremes. I'm starting to get hashimoto's disease but sometimes I have issues with sweating and a fast heart rate.
I did not see your other post but I do know based on my research that there is a lot of info ot there on the subject. You may try to google search " hypo to hyper" and see what comes up or find your 1st posting with all the details and add a comment to the string to bring it back to the top of the forum.
Best of luck.