Suggest Treatment For Rapid Heart Rate And Metallic Taste In The Mouth

I am a 67 year old woman, under alot of stress for a couple of years especially because my husband and partner of 37 years died a year and a half ago, and have been taking a natural thyroid medication for a year and a half. My heart has been racing, I ve been advised by my Osteopath and Naturopath to reduce my Naturthroid (sp?) from 1+1/4 grains to 3/4 grains or even as low as 1/2 grain. I began reducing the dosage 4 days ago. Until today, when my heart started racing somewhat again, I felt better BUT.........here s my question.......last night I made some organic popcorn with brewer s yeast and some butter. It tasted bitter. I thought the brewer s yeast had gone bad. This morning I made a small mushroom and spinach omelet with swiss cheese and it tasted very bitter. I everything I ve tasted tastes bitter. My Osteopath on the phone said not to worry, that it wasn t important. But I m very weirded out. I ve been very healthy most of my life and having my heart race and now having a bitter almost metallic taste in my mounth is scary. Question.....What s going on the cause the bitter taste in my mouth