I started reflective breathing exercises..Are they undamaging?

reading this book and am practicing deep breathing.
Its a simple deep breath, hold for 10 sec and exhale.
I noticed when I put my foot on my chest that my heart is racing much faster than usual when I do this. This can't be good?
I thought these exercises are supposed to relax me not make my heart flog faster
Answers:
Sounds like it may be coming from a lack of oxygen.

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