narcolepsy
"I have EDS and found Nuvigil (250 mg) very effective for remaining awake for the first couple of weeks then my alertness diminished.  I did find that while taking Nuvigil if I took a 20 minute nap in the afternoon, I awoke feeling refreshhed, not groggy and needing more sleep.  The major side effect I experience is nearly severe jaw clenching/teeth grinding during the day when I was awake.  My jaw is sore by 2 or 3 pm every day.  Also, I found it difficult to sleep at night if I took it too late in the morning. I tried getting up at 5 am and taking my dose then sleeping for another hour.  This helped me get to bed earlier at night.  I noticed that I felt more anxious also."