There is a concept in exercise called MMF - momentary muscle failure. This is the point at which your brain is telling your muscles to get back to work, but your muscles are behaving like French students and simply sit down and stop functioning. This can happen as you're in the middle of trying to raise your arm or lift your calf and all the non-affected muscle groups are guffawing and pointing at the offender and using terms like "wuss" and "wimp". Until their turn comes. Which it always does.

Anyway, I believe there is another concept called MBF, for momentary brain failure. Although these become more frequent as you get older, age-related MBFs are usually along the lines of not being able to remember the name of your third grade music teacher, or what you had for breakfast, or whether you really did file your taxes. The worst are the ones that can strike at any age, but usually occur within earshot of someone who has the ability to strongly influence your future, in which your vocal center rebels and decides to disconnect itself, sometimes for no more than a nano-second, from the brainius stupidium preventus lobe and your ears hear your mouth make a statement that is not only unrelated to facts, it is divorced and living across the country from the reality of the known universe. Let's just say that I've had a few days of all-MBFs, all-the-time.