Yes it's when there are high antibodies for your own thyroid hormones, so it's like hypothyroidism but your levels on a thyroid test come back within the normal range. They diagnose it by testing the level of antibodies. Affects a lot of people, crept up on me slowly so I didn't even realise until it was too late. I was waking up after 8 hours sleep feeling like I hadn't slept at all.