Vanderkam points out that surveys in which people are asked to recall how much time they spent on certain activities usually get different results compared to experiments that ask people to keepatimediary.
If cramps bother you frequently, consult with your doctor, who may advise you to keepa cramp diary to try to pinpoint or prevent the problem -- what were you doing at the time, how long did it last, what did you do to make it feel better, what did you do earlier in the day?