If you truly are just looking for averages, Wikipedia is the best resource to start with. The comedown is much more subjective and more severe for different individuals, so there's no way of telling you how it will feel for you. I have a terrible time with comedowns. My best friend always used to just get tired and wanted to take a nap. Having issues with anxiety and depression, as one might guess, tends to predispose people to harsh comedown phases.