I almost always hit a wall of fatigue in the afternoon.  What time of time
exactly it happens depends on when I got up, how well I slept overnight, and
how active I've been.  If I really have to stay awake, I can, witht he help
of caffeine and attention requiring activities, but doing so definitely
affects me until I can get back on the afternoon nap pattern.  For me, it's
from the chronic diseases - RA/PA & fibro.  In fact, when I was on Vicodin
for other problems, I wasn't as fatigued, possibly I slept even better than I
do with Ultram.  YMMV, of course.

ted, that's hard to determine, without knowing what else you are taking,
when and for what reasons.  you might be experiencing a drug interaction; or
you may not be getting enough of the right kind of sleep; or you might have
one of those illnesses that drain energy and need to learn how to pace
yourself.  or, a mid-day power-nap of 30 minutes might be what your body
wants.  and/or there could be any of lots of other reasons.

kate