You may have picked up an "entity" or an energy vampire. This could happen if the client your reiki practitioner had previously to you had one, it was cleared, but then she didn't clear it from the room and it has attached itself to you. It's not as scary as it sounds, it just means that something other than you is feeding off your energy field. It would be like having a parasite (tape worm for example), but on an energy level.

If this is what has happened then I would definitely go to a different reiki practitioner, as your other one has not taken all the proper and necessary precautions to protect you.

Amico,
After my first reiki experience (in a chair) I had some passing pains in my knees.
After my first table experience my left ankle woke me up at night.
Felt like I had on a shackle. Knowing there was no reason for it, I focused on the pain, which broke it up. I could feel the energy running around on the left side of my body, seemingly looking for a way out. I had an "intutive" tell me it was from a previous life experience. Another idea is that I took on, emphatized, with my late husband who had been shackled in a foreign country. (He had to have a skin graph
to heal his wound.)
All this only tells me that Reiki will help clear old debris as well as help
with healing and bringing a sense of well being.
Keep up with the Reiki, it will do you more good in the long run.
Still listen to yourself. Only you know if/when you're ready for it.
You have my blessings, Margie