This is something I haven't heard before. But it is possible that the herbs (which also works as mild intestinal cleanser) dislodge irritants that can wake up the nervous system. You cut the dosage down to half and see if that makes a difference. Also, you may have been doing something else that affects sleep, like eating fruit in the evening.
Yes, you can cleanse the colon more often when you feel the need arises, especially during the change of season (10 days before and after the Autumnal Equinox)when immunity drops and the body goes through major adjustments. This may help with your sleep issue, too.
Also, many people's sleep is becoming disturbed these days due to major earth and climate changes. There is a healing crisis shaking up the earth right now, and her inhabitants.