Happened to my mom (who got Pfizer) and she wasn't nervous at all about anything.

However, she had to stand in a long line for almost 90 minutes, it was windy, and she had no water or food during that time (or even breakfast before going.)

She said by the time she got home, she felt super dizzy, almost empty-headed, and also jittery despite the brain fog. After eating and having more water, then taking a nap, that all went away. She then had about a day of classic side effects like headache, minor chills, etc.

She gets her second dose soon, luckily later in the day and with more food/water beforehand.

So it's definitely not an unknown side effect, but seems to be more rare. I'd recommend eating well beforehand and drinking tons of water.

(of course your situation may vary so talk with a doctor over anything on reddit.)