i have had a few concussions with different severities and problems each time. the first time was when i endo'd on my 80, i remember hitting the ground with my head, and the next thing i remember is comming to with guys pulling my bike off of me yelling "ARE YOU OK? ARE YOU OK?" i tried to ride more after that but the headache was too severe, and lasted for several days. the next one i got was on my 125, at my friends track there is a long 4th gear tapped straightaway which drops into a little ditch and then you jump back out...and the section is followed by a sharp right hand turn which overshot, results in dropping of a nice cliff...only 20 or so feet high, but theres a big shed and a lot of chunks of concrete at the bottom. anyways my back end got kicked up and i was riding a nose wheelie towards the cliff, panicked a litle and grabbed to much front brake. the front end tucked under and i went down hard, tearing the PCL in my right knee and hitting my head pretty hard. my head felt ok at first but within a few hours i had a bad headache and completely lost vision out of my left eye. came back after a couple days, and the ehadache came back every time i rode for close to a month. the latest concussion was at my last race...i endo'd through a whoop section, bike drilled me into the ground and another guy landed on me. i dont remember anything of that except starting to go over, a bright flash, and then getting up and seeing my bike piled up with another and the other rider standing next to me waiving riders to the side. i got up and couldnt breath, couldnt see too straight either...tried to pick up my bike and realized my collarbone was broken...then i collapsed again and woke up to a couple paramedics. my pupils were really dialated and the doctors said i had a concussion, but i didnt have too bad of a headache or anything....the latter of the crashes was one of the first rides on my new moto7...the impact was hard enough to crack the visor and make the paint start chipping but i dont have the money to get a new helmet so i hope its fine...i'm gonna take it with me the next time i get my collarbone xrayed because if you xray it you can check for stress cracks and what not, or so ive heard.