Issue with frequency domain

[funnyshape]

Hi,

I am using pyhrv to extract features from (my) rr-intervalls. Now I am getting this error often:

path/to/file/frequency_domain.py:947: UserWarning: Attempting to set identical low and high ylims makes transformation singular; automatically expanding.
ax.axis([0, fbands['hf'][1], 0, max(power) * (1 + 0.05)]).

I am a bit lost if this means but I get this error mostly when I am sitting still. If I move and my HR goes up the error vanishes.