When they say your levels are "fine," does that mean that you do not have antithyroid antibodies, or that the levels were within the lab's normal ranges?
Looking back at your original post of 4/15/02, you mentioned that your doctor was only willing to test your TSH, that it had been 7.2, then 4.5, and now 1.3; that you had 90% of the hypothyroid symptoms; and that the doctors say it's not thyroid disease because you're in the normal ranges.
You don't mention if you've been on thyroid meds or if there may be any other reason (other medications, supplements, diet) why your TSH decreased as it did. Meep mentioned that antibodies can make all thyroid levels (including TSH) fluctuate, and so you had the Hashi's test.
I know there is limited choice in the British healthcare system, but it sounds like you may need to see another Endo before ruling out thyroid disease. Also, your doctor may not be aware of this, but some patients (about 5%) with Hashimoto's thyroiditis do not actually show elevated levels of thyroid antibodies in their blood tests. Plus there are other forms of thyroiditis where the patient does not have antibodies at all. (This is documented on many websites, including EndocrineWeb.)
Is it possible to try one more time with another doctor, presenting a list of your symptoms, your blood tests, and ask for Free T3, Free T4 and, perhaps, a TRH blood test? Our Information Archive thread has a really helpful Q&A to use when interviewing new docs. And I believe I posted a link to Top Docs in England in my reply to your 4/15/02 message. If it is truly thyroid disease, it would be a shame to delay your recovery further by the sometimes lengthy treatment for bipolar disorder.
While the depressive symptoms of bipolar disorder resemble hypothyroidism, the manic symptoms are quite unlike thyroid disease. And some bipolar meds actually make thyroid disease worse, so you may want to be cautious in ruling out thyroid problems before starting a new regimen.
Hang in there.