These answers might help:

What if I feel worse after a treatment?

Sometimes people experience what is known as a healing crisis. This means that they sometimes feel worse for a short time but this is because the energy acts as a detox on your system,clearing blocked energy channels. This will pass and you will feel much better than you did.Keep in touch with your practitioner if you have any concerns.Reiki can only do good.

If I am a Christian should I have a Reiki treatment? Will it go against my beliefs?

Reiki rises above all religious boundaries. It comes from source,whatever you like to call source--God,Buddha,Allah-etc.  Anything that works for the good of people can never do harm. Reiki only works for good.