Can anyone tell me what a thyroid flare is?

I have an auto immune disease caused from my thyroid. I have super bad anxiety attacks. The only thing I've ever taken that has helped my anxiety and insomnia problems is Klonopin. I still really haven't found anything that helps with the pain from bad flare ups. I usually just lay down with a heating pad. Norco does help but doctors don't like prescribing that. I'm currently taking Mobic and it does help with the day to day pain if you take it regularly. I also take Flexiril when I have the muscle spasms/cramps. It helps but it knocks me out too.