What keeps you awake at night?

I attended a seminar recently where the speaker responded to a question from the audience with "Now that is what keeps me awake at night!" The speaker was implying that the question raised by the audience member was something that worried or troubled the speaker to no end. And they were talking about a specific aspect of the research presented.

When science keeps me awake at night, it's not usually because my results make no sense to me, rather it is usually when I've been stumped by a coding problem and the solution suddenly pops into my head and I'm trying my hardest to make sure I don't forget the solution by the time I wake up the next morning.

And even those instances are rare. Science does not usually keep me awake at night, unless you allow your definition of science to include wondering where the universe came from, if there was anything before the universe as we know it, and what happens after we die.

Those types of thoughts tend to frequent my mind as I try to fall asleep - and I usually push them aside because I've had them enough to know that I never really get any satisfactory answers from them and they usually just end up making me feel sad and alone (even with my husband right there beside me!).

I used to wish that I could see how all this turns out. So that after I die I could be a spectator and see how far the world "advances" and what becomes of us. I think that means I am pretty attached to this world.

Anyway, I wonder what keeps other people awake at night. And I wonder if it is typically related to stressors in our lives, or if some scientists are kept awake by science because they simply love thinking about it.