I've been on the drug for about 10 days. As a runner, my resting pulse rate was usually in the 40s already. Now it's commonly in the 30s, and my energy is down noticeably. When I run, the lack of energy is particularly noticeable. I suspect the 5K I ran in less than 23 minutes last month will take me more than 25 minutes this week. Are there particular risks to pushing myself? Will my body eventually adapt to the lower heart rate?