I work a rotating shift with 7 days off every month. I just started the Nuvigil for Shiftwork Sleep Disorder, and I find it very effective for keeping me focused (and awake) for 16-18 hrs when I'm working. I've had one day off since I started the meds, and I COULD NOT go to sleep for 17 HRS after taking my dose! So what about my days off when I don't want to be awake that long? Will the length of effectiveness shorten with use? Can I NOT take Nuvigil on my days off in order to get additional sleep?