SPEAKING FROM EXPERIENCE 
i got a pretty bad concussion playing rugby about two years, ago...it was healing, and i went skiing and fell and slightly hit my head again when i tipped over on a bad landing...didnt think anything of it, but felt kinda weird, like i was coming down from a concussion (not sure if i explained that well)
regardless, had a couple drinks and smoked a little like a couple days later and felt MAD WEIRD, like, couldnt focus on anything and it felt just fucking weird
waited a couple days and smoked again, completely bugging the fuck out cuz my head was SUPER FUCKED
the next day in class, the same "hallucinations" (it kinda felt like a light shroom trip, walls moving slightly and such) and i wasnt high or drinking or anything and i fucking lost it and went straight to the hospital, where they told me i had post concussive syndrome, something where since my brain was recoering from the concussion, i rattled it again, and then proceeded to drink and smoke (altho not much) i just fucked myself over
it healed on its own and i was fine after a couple sober weeks but shit man i dont ever wanna feel that way again, especially the daylight one
i know, im an ass for drinkin and smokin but shit, thats what we did after games and such for rugby