I did get a all day headache after a Bowel Cleanse last week. I mean, from the time I did the cleanse until I went to bed.
I read somewhere on the Bowel Cleanse page on curezone that headaches among other symptoms are caused by toxins that leak back into the system. One piece of advise given was peppermint tea, which I drank the next morning and that helped. After that for a few days I would take a hot bath right after my cleanse to sweat it out a little and that made me feel much better.
Everyone is different so I do not know what to advise except research research research!