[bleah1000]

I think the problem is that even with breaks, you can still be mentally exhausted by the last interview or two. For a normal work day, I wouldn't expect people to switch between writing completely different algorithms and problems so often. In a day of interviews, switching to a new problem five or six times can be exhausting.

Make sure your interview process isn't stacking too many in a row, or the signal from the last few is going to be pretty bad.