Erin warned that I'd feel a little sore, similar to how I'd feel after an intense workout. I was more sore after the first session, which Erin said was normal; the more sessions you do, the less sore you'll feel.
She said I could take an ibuprofen if I wanted to, but it wasn't bad enough that I needed to. I did feel sore while sleeping and felt a little sore the next day, but it was gone within a few days.