Nah, it's something totally normal. The adrenaline rush, the anxiety, the power and stamina you have during the exam to get everything completed is WAAAY too much for the body to handle.
You are sooo much more better off sleeping the rest of the day, taking a break, doing something that doesn't require too much, and do more work the next day cause you're relaxed, than push yourself to do work in the night because you don't think you "should".
Trust me, don't feel bad! I've had a day between english and biology and didn't do work those nights
