Katerina,
Hi,
The energy we access through Reiki practices is only one aspect of the entire complex of energy which is ULE. And, the intention and mindfulness we are able to muster and apply also affects the nature of the energy(s) we bring to any session. In Reiki, the goal is to keep personal energy out. In other practices, personal energy is part of the method. So, it is also possible that the variations in heat you sense could relfect some variation in the intention you had at the time and mindfulness with which you applied it.
Remember too, that the amount of energy that is actually received by the "client" is a direct function of how much energy that person is accepting through their intentions to use the energy and the mindfulness he\she applies. Thus, if the person cuts back on the amount of energy accepted, the flow will diminish and it is possible that you may then sense this as cooling of your hands.
Cheers,
RC
