I think it is very likely that many people who suffer from morning fatigue which eases gradually throughout the day may have low potassium levels. I used to assume that morning fatigue was probably a symptom of low cortisol but I now think that low potassium is a lot more prevalent than generally recognized. It's been true for me and a friend of mine whose morning fatigue has greatly lessened since she started taking extra potassium. I think potassium levels tend to be lowest in the morning (that's what I've experienced) and then when you eat etc. you gradually raise your levels. So if low potassium is causing fatigue, it makes sense you would feel better as the day goes on. However, if you never get your levels up to where they should be, you will always be tired in varying degrees - fatigue is a major symptom (among many) of low potassium. I first started to become aware of potassium and its importance after reading about Freddd's B12 protocol. My potassium levels tanked after a couple of days on methylfolate - I had severe fatigue and lethargy - which went away as I gradually got my potassium levels back up through supplementation. The really interesting thing for me though was that that awful fatigue was very familiar - I had had it before but never knew what it was. It was just another weird awful CFS symptom (or so I thought) that would appear from time to time, and then go away just as mysteriously. On blood tests my potassium levels were always on the low side of the normal range so I think the blood test is almost meaningless unless you could have it done every day (sort of like with a diabetic perhaps, where one blood sugar reading obviously will not be true the next day or even the next hour) An easy way to find out if you need more potassium is to take extra and see how you do. Low-sodium V8 is a really good source of potassium - an 8 oz. glass has 900 mg. and is only 50 calories. I was taking a lot of potassium gluconate and still having trouble getting enough potassium, but since I started the V8 (2 or 3 glasses a day) plus some extra potassium capsules, my levels are better. For some reason low-sodium V8 has a lot more potassium than regular V8, which has around 500 mg. per 8 oz.