Hello,
I have Hashimoto's, too, and have been taking synthroid for 15 years, I am 49 years old and go in annually to see and endo. doc who monitors my dosage, levels, etc.
No problems at all until I started experimenting on my own with progesterone cream, to help with premenopause symptoms. 2 months after continued use of the cream, I started to get scary heart palpitations at night, combined with sleepless nights, too. I think it was the progesterone cream, my endo agreed.