What happens if I don’t “feel anything” after a Reiki session?

Sounds like it didn't work. From my experience the patient should feel lighter. Perhaps try another provider or modality.

There are some people who don’t feel an immediate change after a Reiki session, and
it’s nothing to worry about. It doesn't mean that it hasn't “worked,” just that it's taking
longer for energy to settle in. Ideally, you want to give yourself a little space after a
session to let it integrate: take this time to drink some water, stretch, walk, or nap if you want. Often people notice that they feel better later on in the day, or when they wake the next morning.