Yea - i'm pretty sure that it's possible. I'm not a doctor or anything, but got 3 sports related concussions in a 2 month period of time. It has been 2 months since the my last concussion and I still get bad head aches and occasionally get really dizzy and feel like I could pass out. I had several ct scans and a few eegs and they all came back clear. I was told (by my doctors) that even though the mri and ct scan and eeg and other tests came back ok, that that did not mean that I was ok. I still had really bad post concussion syndrome and I have to sit out all of my track season this year =(