I was just bitten by a radioactive stopwatch, gaining the voluntary ability to experience time at twice the usual rate. While doing so, for every second of real time, two seconds occur within my body.
Like previous question-askers, I'm effectively twice as strong, and outside forces affect me half as much. My voice is an octave higher and everything I hear is an octave lower. Breathing is more difficult and everything feels cold. That last part nearly killed me, but I rigged up a fancy respirator with heated high-pressure oxygen.
My current concern is vision. Light wavelengths double as they enter my eyes. Visible light becomes infrared, UVA becomes red, UVC becomes blue. Expanding on this answer, what does the world look like to me? What useful things can I see, and what commonplace visual features are indistinguishable?