What underactive thyroid can involve
An underactive thyroid means the gland is not producing enough hormone, and the symptoms arrive slowly enough that people often put them down to age, stress or winter. Fatigue, feeling cold, brain fog, weight changes and low mood build gradually, which is why the gap between first noticing and being treated can be long.
Once treatment starts, the question becomes whether the dose is right, and that is answered partly by blood tests and partly by how you actually feel. A record kept over weeks gives the second half of that picture, in your own words, rather than trying to summarise it from memory in a ten-minute review.