i see. some people get really severe reactions though, like the people here talking about a week long; does that explain those cases? is there no relation b/w vaccine reaction and reaction to the actual virus?

Well, I personally had a >2 week long reaction, and after the second shot, was informed that yes, it probably was some sort of allergic reaction. What was it? We still don't know

Regarding correlations between the two, it's a bit difficult to tell. After all, you can't really get a correlation between the intensity of vaccine reaction and actual virus exposure for... obvious reasons.

However, (I'm a bit rusty on my allergy and autoimmunity, so if someone catches a mistake, please call me out on it) allergic reactions and the viral reactions tend to present themselves differently. The common image of swelling and inability to breathe are almost completely associated with allergy, while the fever, tiredness and so on tend to be more standard.