I am a 33-year-old female who has been on a fitness program for five weeks, using the Couch-to-5K running program. I have been wearing a Polar HRM for the past two weeks and try to keep my heart rate in the 150s.
Today, I stepped up in my program from two 8-minute runs separated by 5-minute walks to one continuous 20-minute run. In the first minute of my cool-down walk immediately following my run, my heart rate spiked up to 200 and I felt lightheaded. I panicked a bit, but kept walking, and it came down over the next minute. By the end of my 6-minute cool-down, my heart rate was back to 120.
The X-factors: I am typically diligent about my nutrition and hydration -- except for the past few days at a family vacation where we ate things like barbecue and pizza -- and I was sedentary the past two days.
This has never happened before. Is it a fluke, or is it a sign of something serious?