My husband had the twice a day radiation sessions a couple of times during his first radiation treatment as it spanned the Christmas and New Year Holidays when the hospital was closed. You might feel a tad more tired on the day after than on the other days. Sitting around waiting for the second session could be a pain. If you are within driving distance, you may want to consider going home and coming back later. Check also if the hospital has a radiation care clinic that you can go to and lie down to rest in between the sessions (we have this at our hospital). It is not a big deal, don't worry about it.