Spike in Heart Rate During Exercise Cool-Down

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?

[nicolette36]

i would keep an eye on it,maybe its just a one off isolated incident but that is how my svt started off,after a workout.maybe keep a diary of when this happens and take it from there.i hope it doesnt happen again though.

[Mario_101]

I'd see a cardioligist to rule out any heart problems