I feel dumb as a stump

I have had this nagging feeling since my return to the world of academia.
My theory is that it is because:
1. I haven't been doing ANYTHING for the two and a half years while I was supposedly working
2. I didn't really learn anything back in undergrad years and abused the system to graduate with first class honours and top BTech IT graduate award (shared)
3. CS at UIUC is just on a whole another level and I'm just a "normal" person
4. the concept of testing one's understanding of a subject with deliberately tricky questions in a restricted timeframe itself is flawed
5. I'm speaking English while people here are speaking American
6. too much coffee causes brain shrinkage
7. I'm in fact a stump disguising as a human (DING DING DING!!)
8. Maybe I shouldn't be wasting time blogging and study given that I have another exam next week

OK, I'm just frustrated with the midterm grades I got so far and playing the blame game for my lack of intellectuallability, but I feel lost as to why something that worked before doesn't work anymore. I don't know how else to study... :( I know, graduate study is different from undergrad, and UIUC being UIUC, there are just so many people from all over the world who are just plain smarter than I am. I accept that. It could be a bad case of imposter syndrome that I am experiencing now... What can I say, I'll just try harder... Sigh...