Hi, You are having a low blood pressure with increased heart rate. Your blood pressure medicine could be lowering your blood pressure (BP) too much and your heart rate is going up to compensate. You may be a little dehydrated as a similar picture is seen in that case. I would advise you to see your clinic or doctor and have them take a few BP readings and decide if your medication needs changing to a lower dose perhaps. They should also look for infections and would need to take some bloods for you. If your Thyroxine dose was too high it would cause high blood pressure and high pulse together. But your blood pressure tablet maybe masking an elevated blood pressure so your Thyroxine dose may need decreasing if that is the cause as well. Hope this has been helpful. Let me know if I can assist you further. Regards, Dr. Raboobee