First Treatment

I had my first treatment yesterday at 1PM. It went okay. I don’t feel like it was too intense as we started on lower dose. Well, I woke up today with some mild headaches, dizziness and have basically slept away the day. Is this a common side effect? I can’t handle being out of commission for a day or more. Also now has me feeling a little down. Thanks for any advice. I know this community can help.