Chad Orzel has an illuminating article up up on his blog Uncertain Principles talking about the misconception the media has that all physicists do high energy particle physics and then talks about the things that keep low energy experimenters up at night(spoiler: it does not involve blowing up the solar system or accidentally creating black holes that will swallow our planet). From the Article:

Taking Data: I’ve done my share of late-night data acquisition, mostly for a combination of the second and third reasons above. In grad school, the main experiment I worked on took data on 45-minute cycles, which needed to be paired up, so the time for a single useful data set was an hour and a half. That involved a lot of late nights at NIST.

Planning Experiments: The one time I vividly recall being kept up at night by a physics problem, I was trying to do calculations in my head to determine whether I ought to completely and radically revise a grant proposal to do a different sort of experiment than what I had planned. This was a week or so before the deadline, and it had occurred to me that I could use my proposed apparatus to do a slightly different sort of experiment than that described in the many pages worth of proposal that I had already written.

I spent a couple of hours lying in bed, trying to do calculations in my head to determine whether I could reach the temperatures and sensitivities required to make the measurements needed. This didn’t actually get anywhere– I ended up having to call a couple of other people on the phone, before deciding that it wasn’t a sure enough thing to justify the hasty re-writing– but it definitely did keep me up at night.

So there’s a list of physics-related things that have literally kept me up at night. You’ll notice that none of them involve particle physics, quantum gravity, or multiple universes– while the Big Questions are interesting, they’re generally too abstract to keep me engaged at the level necessary to keep me up late. If you suggest a way to answer one of those questions with a low-energy AMO physics experiment, I’ll happily lose sleep trying to make it work, but absent some tangible connection to empirical reality, I’m just not interested enough to stay up past my bedtime.

I suggest going and checking out the rest of the post if you really want to know what keeps regular physicists up at night.