Hi Flutterby,
I agree with the others. If you are ever uncomfortable you have the right to end a session, especially if you are new to Reiki.
Your energy system may not have been ready to have that much strong energy flowing into you. It can be a shock to the system.
You might try speaking with your guides. Tell them you feel uncomfortable and can they please adjust the energy for you. Guides, teachers, guardians and angels are marvelous creatures. In energy work they can become your best friends.
Blessings
Ashkee