The brain of an ER nurse is not always a fun place. Especially at triage, my job is to always consider the worst possible thing that could be going on with a patient, and sometimes it's hard to turn that off when I go home.
When I wake up at night feeling crappy with back pain and bladder pressure, the first thing through my head is, "Suspected pyelonephritis. Start IV fluids, antipyretics, collect a urine sample, check WBCs, anticipate IV abx and possible admission."
Then of course I wake up a little more, and I relax because what I really have is a cold and a back strain, and I go use the bathroom then go back to bed. But it's hard getting back to sleep after that little adrenaline spike.