Hmmm. I went out to work in the yard yesterday mid-day. I was feeling just fine. After about a half hour of relatively light exertion, I felt as though I had been working all day. I went inside to regather my energy and promptly nodded off for over two hours. Since I do physical work every day for a living, I can usually power through almost anything, including hangovers and inadequate sleep. Yesterday was like a knock-out punch.