I try to get a flu shot every year. I got one last week, since the flu season is starting and don't want it also because I would be afraid a flu could be rather covid-19. I had no issues this year or last, but I know what you're referring to about the slight redness on injection site and "heavy arm". It will surely pass. If you experience anything far worse, or if the discomfort persists a long while, you might wish to check with your doctor or pharmacist.

Are/were you a generally high energy person, by nature? I'm excluding any medication sedation and referring more to your baseline energy levels.