[jfengel]

No, it's not just you. I see variations of this all the time on Quora. And even more questions about the even-more-remote Heat Death of the Universe, and how we might go about preventing it.

I've put a little bit of thought into where this might come from. It's clearly not a realistic thought. There is no meaningful way it impacts your life. Both evolution and technology progress on vastly faster time scales, and so there is nothing for you to gain from thinking about it now.

Pop psychology suggests that it's perhaps depression or boredom. They're catastrophizing to avoid thinking about something else.

If it's causing you distress, you could consider seeing a therapist to get to the root of the problem (which almost certainly has nothing to do with the sun). If it's merely a way for you to amuse yourself and isn't making you unhappy, it's no worse a hobby than a lot of others I can think of.