Doctors tell people all the time their thyroid tests are normal when they are not,
Exactly. These tests frequently miss cases of hypothyroidism. The short of the two reasons for this is the stress of going to the doctor can lead to a temporary rise of the thyroid hormone levels putting it temporarily in the normal range. So when the read the test it looks normal. Then you go back home and relax and the thyroid hormones plummet back down to their subnormal range. The second reason is that chronic stress elevates levels of reverse triiodothyronine (rT3), which is biologically inactive. The rT3 will lock up T3 receptors though preventing the use of T3, which is more biologically active than T4. Therefore you can have normal TSH, T3 and T4 and still be hypothyroid if your rT3 levels are high. Doctors rarely test for rT3 levels. In fact I am not sure if most if them even have a clue what it is.