It always comes to mind how many fictional immortal characters and creatures just basically choose to go into an eternal slumber. There seems to be a de facto consensus that it is actually pretty boring stuff.
Perhaps it is a way to deal with limitations of their brains. They usually have finite brains, which presumably have a limit on how much information they can store and organize and process.
Suppose you are an immortal working on some long term goal, some plan that will take a few hundred years to complete. It is a complicated plan and you will need to keep it all in your mind, along with its history as it progresses, in order to guide it to success.
If you try to lead an active life throughout all this, perhaps your brain will acquire too much irrelevant information, interfering with your ability to carry out your plan.
So you sleep for decades at a time, just waking up long enough to check on the plan, learn about changes to the world since your lest check, and make adjustments. Then back to sleep.
