I should have thought of the blood sugar idea. My wife used to take my son a glass of orange juice when she woke him for school. Otherwise, he was grumpy until after he ate.

Fasting hypoglycemia is not uncommon. 7 to 8 hours after a meal, the body often needs to start relying on the liver for energy. For some, this is not adequate.

I need to eat before going to bed or I struggle to sleep through the night as I hit that fasting hypoglycemia by early in the morning.

MM, I was alluding to Leddy's concepts when I mentioned heart rate and headaches. His primary indicator for lowering exercise pulse rate is headaches.

btw, Many use caffeine to force through this low blood sugar issue. This can cause even worse problems over the long run.