What Causes Excessive Sleepiness And Sudden Body Tremors?

On rare occasions, about once every 2-3 weeks, I have an uncontrollable need to nap and am cold to the point of almost shivering. The room can be 72 degrees, and I have had a full nights sleep. I do not have sleep apnea (I was monitored). The symptoms disappear after a 30-90 minute nap, not to return again for weeks or a month. It is dangerous if I am driving as I must pull off the road to rest. Caffeine can overcome this sometimes but the alertness is minimized during this period. This has existed in me at some level since childhood - but now at 55, it s significantly magnified in intensity - but reduced in frequency. Finally, my blood pressure is 120 over 75 (although when I was training for the half marathon it reduced to 110 over 60).