Dear Techbunny,
That old saying, "Use it or lose it" only applies to Reiki as far as the perception of, the sensation of the energy flow. After being away from a group Reiki experience for some time I went to a share & was told that my hands were really hot ( I felt no heat at the time). This mimics what was witnessed with other Reiki practitioners when I was new to Reiki & active in a group.
In every moment of our lives there are chemical, mechanical, hormonal energy reactions taking place in our bodies but we are not aware of it & thank goodness for that! We would be distracted & unable to focus on other things if we were consciously aware of all of that energy.
Dust off the manuals if you need a refresher. Do some preparation work to open yourself up to the energy ( I like the Reiki shower technique but everyone has their own preference). Reiki your self, do some long distance work and/or join a share. You will be fine.
peace & joy,
holobon