What exactly is subclinical hypothyroidism?

High TSH but with: Normal thyroid levels. It "usually" entails a symptom free state but if the cause is autoimmune in nature, there might be some signs or symptoms. The thyroid profile will need to be monitored regardless.

Still hypothyroidism: It is where you TSH is normal but your free T3 and reverse T3 are not normal. Need Armour Thyroid to treat this, not synthroid (thyroxine).

Undiagnosed hypoT: Hypothyroidism can be primary - caused by a weak thyroid gland or secondary to other hormonal problems, like a pituitary problem. Or your thyroid can become dysfunctional secondary to high insulin, estrogen or cortisol. If you have functional hypothyroidism, this problem can go undetected by routine screening tests. More extensive testing can often reveal abonormalities. This is very common.