Well it is hard to know for sure as everyone is a bit different. Given that, I have the following to say.It should not effect alertness or how you sleep. Basically what the fiber powder does is replace something that used to be in our diets before we learned to process all the goodness out of it. If it is a product that can make you more gassy (like psyllium based products) you may have symptoms of gas for the first couple of weeks of sustained use. For most people this symptom subsides (I find Gas-X or products like it helps with that, and they have no known side effects so they seem pretty safe). If gas in the GI tract makes you very uncomfortable, I would stick with non-psyllium based products.What usually happens as you increase fiber is that your stools have more bulk. So if you are D they are more solid, if you are constipated they are softer and easier to pass. (the fiber absorbs the excess water in the colon and with Constipation it prevents the colon from removing as much water from the stool). How long it takes to see a difference in them will depend on your transit time, and the dose you are taking. If you are ramping up the dosage slowly you may not notice much of a difference.For some people adding fiber can bother their IBS. When I had mild symptoms (most of my life) it made me feel better. Once my IBS got severe (major league double over clutching the belly spasms) fiber seemed to make my cramping slightly worse. Now that I am back to mild it helps.K.