In the past year or so I've noticed that I am able to nap at the end of the work day. For various reasons I do not get a full 8 hours of sleep most weeknights, and end up sleeping in a bit more on the weekends, both of which set me up for the "groggies" at about 4:00 pm or so. It would be prudent for me to get to bed sooner, keep a regular sleep schedule, and not have to travel quite so much. Hotel beds and time changes screw me up for sleep a lot as well.