Before your first dose, you still have a brutal headache. It's not necessarily the meds that make your brain foggy, it's mostly that you can feel your brain bouncing against your skull every time you try to think or breathe.

Yes, because if your headache is so bad, you end up accidentally ODing on meds, you are clearly able to think about researching stuff and realising that you aren't sure. It's not like your thoughts are limited to "I'd do anything to make it stop" and "this looks like it kills pain, gimme".