You gotta hydrate a lot. Ideally replace sugars with fats (good fats, like the natural ones).
Could be related to a bad pH levels (not enough acids), so make yourself a huge glass of orange-based electrolyte juice everyday. Adding turmeric or cayenne pepper and black powder will also help for the brain-blood barrier. Nausea/dizzyness might mean that there's a problem with oxygenation (blood-oxygen levels).
For a quick fix Aspirin does help for many issues like these, but don't take more than 2-3 times in a row.
Breathing exercises and warm up before workout can change a lot too.
Thanks anon gonna try all of these things! I have a list of possible solutions to my post-workout problems now, gonna test one every time I exercise until I find one that works