I have an open notebook on my desk which I use through the day to jot down stuff to investigate, reminders about meetings and appointments etc. It's always open

I have an open notebook on my desk which I use through the day to jot down stuff to investigate, reminders about meetings and appointments etc. It's always open on the current day. If I have this fresh idea in the middle of the night, my main anxiety seems to be that i'll forget it tomorrow, so I find just adding it to the list for tomorrow is enough to ease that concern, and allow me to get back to sleep. Failing that, get up and get on with it, feel shit for the afternoon, but just keep going through to your normal bedtime, and obviously avoid power tools in the afternoon :)