I interviewed with Mozilla back when they were working on Firefox OS. The first question was to write a linked list in C++. Easy, I actually practiced that ahead of time. However, I forgot everything and started sweating profusely (Thankfully it was a phone interview). The interviewer was nice and tried to help me get started but all I could think about was how stupid and screwed I was.

Since then, I've found that I need to practice extensively so that I can still function when my IQ drops due to the stress. It reminds me of, "Under pressure, you don't rise to the occasion, you fall to your level of training."