Every Evening My Heart Rate Increases And I Can Feel

Every evening my heart rate increases and I can feel it pounding in my chest and neck. I just had my thyroid checked and I have decreased the amount of thyroxine I take in half. I have taken he new amount for about 6 weeks and I just had blood work done and was told my level was good. I have also had high blood pressure problems, howeve, I am now on medication and when I checked it last night it was normal. I was having the same symptoms last night and that is why I checked my pressure. My heart rate was 103 and I had been laying around watching TV. Not sure what to do from here.