Everybody knows this hour. The house is silent, your heart is going a little too quickly, and a small mistake that you made in 2014 has come back to visit.
Notice it
Start by doing nothing in particular. Sit somewhere comfortable, put your phone in another room and notice how long it takes for your hand to reach for it anyway. You are not failing. You are collecting information, which is a kinder and much more useful thing to be doing.
Nothing looks the same at breakfast. Remember that at three.
Name it
Psychologists have found that simply naming a feeling can take some of its heat away. The technique seems almost too simple. Yet there is a real difference between being angry and noticing that there is some anger around today, and that small distance can make a long afternoon survivable.
Begin again
If it has been weeks and things have not lifted, it is worth talking to someone qualified. Your general practitioner is a good first stop. It is not a dramatic step, nor an admission of anything. It is what you would do for a persistent cough, and a mind deserves similar treatment.
And then, tomorrow, begin again. The people who say that they have got this all figured out have usually got something for sale. For the rest of us, it is a small practice, repeated often, frequently abandoned and always available to be picked back up, with no penalty.

