The potassium connection only exists for those very low in B12 levels to start with, who had anemia as well.

High injectable doses of B12 which may be given daily in the beginning, will stimulate the bone marrow to make more red cells quickly. Red cells contain alot of potassium and since this mineral is not stockpiled in the bones like calcium is, a sudden need for it may develop.

It is not going to happen the same way as a gradual oral supplementation of B12 would be vastly different.
I don't get the energized thing with B12 at all. Some people don't.
You might want to eat potassium rich foods, as many people don't, and the new nutritional target recommendation is 4.6 grams a day.
A can of V8 juice is very high (about 600-800mg)...higher than bananas, etc. The low sodium one is 1100mg! This is easy to do, and more effective than OTC supplements which are only 99mg. Gatorade only supplies 30mg a serving...useless.

But we all do have a circadian rhythm of cortisol production. It is highest in the morning after breakfast and a second less high spike after dinner. It is lowest at 4am or so (and this is when people most commonly die in hospitals or in their sleep) and a second less low dip at 4pm in the afternoon. This is why I believe the British have "teatime". A snack at 4pm tends to take away the subjective feelings of being low when that cortisol dips.

My guess is that when people are low in B12, they feel awful most of the time, and the 4pm dip is just more of the same. Improve things and get going nicely, and these patients would feel better for most of the day, so when the "dip" arrives it is more noticeable.

B12 responsive is highly subjective and always has been. Doctors know this, and in the historical past used to use it as a placebo treatment for any complaints of "tiredness" and fatigue that patients would complain about. It was so abused this way that the medical community overreacted and slapped sanctions on doctors for using it this way. So today, we see a reluctance to even test for it, or use the new lab ranges that are more accurate, because the med schools still teach that it is a mostly useless treatment and not to do it! To this day many doctors ignore elevated MCV in the blood work which is a direct hint that B12 is low!

I received the blood work of my cat, which was done before vacation. And the vet on the phone said it was all normal. But it is not...HER MCV is elevated! And I looked that up on the net at a Vet site, and MCV is elevated in about 50% of hyperthyroid cats. And she has that nodule on her left lobe he found. So tomorrow, I will be going to a cat specialty vet, and I just bet she gets some B12 injections! (I saw another owner picking that up for HER cat one day in the waiting room!)

I am still reeling that our own 13 yr old cat may need B12 ---and that her tests show what happens to humans as well!
I'll post tomorrow afternoon, as her appointment is at 10am.
I might have to wait for her bloodwork. (this cat vet does some right there, and sends other things out to a lab).