That's an issue with blood transfusions ... Well, one of many ...
As far as the low BP thing, yes, drinking can cause you to be unbalanced ...
The excessive water in the beer, yet the alcohol as a diuretic, can cause its own issues ...
Thing is, is you drink a lot, and have a limited sodium diet, the diuretic (alcohol) does two things ...
1) Unbalances your electrolytes (which can cause those symptoms)
2) Elevates your ketoacids ... This can cause complications such as raised ionic content in blood
(emulating, and eventually causing drops in sodium/electrolytes, thus causing lowered blood pressure)
It's not a coincidence that when you drink, the only way alcohol escapes your body is after it's burned off
(as it's a "sugar") and causes a form of ketoacidosis/same as a diabetic that's hyperglycemic ...
It can be hard for us medics/police/ems to tell if someone if hyperglycemic or drunk; it's the same basic
smell and causes the same basic symptoms (disorientation, dizziness, fruity smell on the breath, etc) ...
What you've described can go in different directions from your symptoms, however, collectively, make a
little more sense ...
The others, since your transfusion, are explained with the lack of total testing of the blood ... Whatever condition it was truly in ...
Read this real quick ... It'll explain at least part of it ...
https://www.mayoclinic.org/diseases-conditions/diabetic-ketoacidosis/symptoms-causes/syc-20371551