This morning started out on the wrong foot: I was awakened at 6:40 a.m. by what sounded like a very loud lawnmower in the middle distance.
I was too groggy to make any coherent sense out of anything, but I did figure out why the noise was stressing me out so much: it was reminding me of the Loud Car Guy saga.
(Short version: Back in 2003, I had a neighbor who insisted on revving his extremely loud engine right outside my apartment window every weekday morning at 6:30 a.m., and he was really nasty to me in various ways when I tried to get him to stop. It eventually led to my moving out, in part because the apartment managers indicated that I was the one who was being unreasonable. On the plus side, that was when I bought a condo, which probably indirectly led to my buying this house, so I suppose it all worked out in the end.)
The stress that being awoken by a revving engine causes me has diminished quite a bit since then, but it's still there.
I turned on the "brown noise" track in the Ambiance app, and turned the volume way up, which helped but didn't entirely mask the noise; and I discovered again that under certain circumstances pressing a pillow to your ear can make an engine noise sound louder instead of quieter. But after about ten or fifteen minutes, the engine stopped or maybe I just calmed down enough to get back to sleep. Woke up again a couple hours later, still groggy but much more relaxed.