Last year, I revalidated my IMC for the xth time and can assure anyone worrying about how knackered they feel learning, that I still feel knackered when I go up for checks with an instructir prior to each test.
I was told by my original IMC instructor (a Mr C Ladbrooke - if anyone knows of his whereabouts, let me know by pm, I still hear his voice every time I fly an approach), that if when on instruments, if you go more than 10 seconds without checking someing, you are doing an inadequate job.
Its worth it though !!