The second shot is a booster, so the first shot should have had few symptoms but sort of primed the immune system so to speak, while the second shot triggers it in and makes you ill. Except if you have a more active immune system, that is. Then the first shot would lay you out, and the second shouldn't have any severe symptoms, since you already triggered it.

So for the vast majority of us, safe to assume at most one bad time between the two shots. Usually the second, sometimes the first. Most of the time it's neither shot.

Far as I know, at least.