What you are describing is essentially sleep deprivation. True narcolepsy in the horse is extremely rare, and documented most often in foals, all of which seem to grow out of it after a few months.
Horses do require about 30 minutes a day of deep REM sleep. And contrary to popular belief horse's do not "sleep" standing up. They simply rest.
Here is a link to an article by Dr. Joe Bertone who has been studying the issue in horses for a number of years. He's an equine internal medicine specialist at Western University in southern California. Click Here
. Here is a link for a few horses demonstrating it in their paddock Click Here
If you have not seen your guy lay down, there is generally an underlying cause. This cause can be anything including behavioral (not having a secure feeling, not being in contact with a herd, ect), environmental (not feeling comfortable that he can lay down in his stall, see other horses, uncomfortable ground), or physical (lameness, soreness issues, ect.).
Often times, placing the gelding in with a dominant mare or even just another horse, changing the stall/paddock setup, moving stall, moving pastures, etc can help. I hope this helps shed some light on the issue, and that it opens a door to some reading as it is much more complicated than my short description.