It is possible.
Energy is supposedly infinite, but your system may not be in resonance with the whole spectrum of it. So, perhaps you're only receiving a subset of the whole range of frequencies?
I think by practising empathy towards everything, the body will probably accomodate to receiving a wider range of frequencies.
Another possibility would be that it's not the energy that is drained, but the ability to use it. Or in other words, the body is not used to prolonged concentration.
