I was told i might have a minor concussion i guess. i passed out and the er called it convulsive syncope? its been two weeks since then and i drank some coffee this morning and i felt brain fog like a lot. why?

Coffee should not have any effect to a concussion which occurred 2 weeks before. With that diagnosis from ER you were likely referred to a neurologist for a follow-up so you need to do so. It could be just a coincident that you have brain fog at the same time you drink coffee. Good luck.

Consistent with prior advice, you should seek neurological consultation and clarify what previously occurred. It is not evident from your description as to whether you fainted, had a seizure, or had a head injury prior to or subsequently. Brain fog could be due to any and all. Get this addressed. Avoid driving until clarified.