Another here on 150cg. I've never found Thyroxine a silver bullet, I've probably been on it for getting on for 25 years now. Before I was diagnosed all those years ago, I had days when I feel I was wading through cement, the only way I can describe it. I have varying days now, sometimes I feel fine others really sluggish, I can't always pinpoint what precipitates that. Exercise can help, usually I try to swim 3 times a week, but am inactive at the moment due to a broken arm.
In America some people who have hypothyroidism have the condition treated, with "Armour" derived from pigs, rather than the synthetic form we take here. I read that is more succesful in treating the ongoing lethargy many sufferers experience but it's much more expensive and not available here, or wasn't when I read about it last. Interestingly when Hilary Clinton was running for president and made her medical records public, that was what she was taking.
I wish you luck with your appointment Nan Kent.