Midnight makes every problem look permanent. Make the big decision after breakfast.

Late at night your ability to imagine things changing is at its lowest, so whatever is wrong presents itself as the permanent arrangement. Nothing about the problem has altered. The equipment you are using to assess it has. Morning does not fix anything either, and it does restore your sense that the situation has a future.

Make a rule that nothing important gets decided after a certain hour. Write the message if you need to and leave it unsent. Read it again after breakfast, and if it still looks right you can send it then, having lost nothing by waiting.