When we're tired and frustrated we're in far from the best state to solve problems that are bothering us. Yet at night is the time when worries can rear their ugly heads and demand our attention.
In times such as this a useful technique is put these thoughts and worries in a safe place to be dealt with later, when you're awake and alert and far better placed to find a good solution. One approach is to put a notebook and pen by your bed, so if you find yourself running through problems that need to be solved you can easily jot them down, to be dealt with in the morning by your “future self”.
But even if you don't have a notepad to hand you can mentally put those worries away for a future you to deal with. With your eyes closed simply imagine a sturdy glass box floating above your head, attached to the wall. This is your thought locker. Now open the lid of that box with your mind, put the bothersome worry into the box, and let the lid shut firmly behind it. With the topic trapped in that sturdy locker, ready to be looked at afresh in the morning, you can focus on the most productive thing you can do – rest and relax. If any further thoughts appear, open that lid and drop them in the locker. And if you find yourself returning to any topic, just remind yourself that it's already safely in the locker to be sorted out in the cold light of morning.