Because of one reason or another (sometimes out of my control, sometimes out of my own distraction) I end up sitting late at night. Probably not the best idea because I often become distracted with just how tired I am at that moment. Letting it be only goes so far against biology and me falling asleep, head against the wall. To balance this, often times I will gassho, and get up to do kinhin for a minute or two then return back to my zafu.

Question is: is that advisable? I could see how it could become a habit to just kill time but occasionally it really helps pep me back up for the last ten minutes or so of sitting. Really this is only an issue at night, during the morning it's not difficult to wake up.