I didn't have Pfizer, but it's probably worth being prepared for the fact that you might be ill. It's not going to be the same experience for everyone. Both me and the other half had AstraZenica, and the next day we were both more ill than either of us have been in a long time. But I know plenty of people who've had no problems at all with AstraZenica. I see the same thing with Pfizer too.