Thankfully I don't have time sensitive loads so I always take naps if I'm driving at night and got bad sleep before the shift. usually 1hr is good. just sucks when even the rest area ramps are full so I have try to find a suitable ramp to sleep on.
I have pulled into a rest area in the middle of my shift cause I didnt sleep good the night before. Like others have said, 1 hour nap can make a difference. Still had a 97% on time delivery rate when I got sick while with Marten. My dispatcher knew if I stopped, there was a good reason.