Check engine light -- now you see it, now you don't

2010 Prius III, 101K miles. It sat for three weeks without being driven, though I started the engine and let it run for a few minutes three or four times.

I took it out for a drive this afternoon and noticed the check engine light was on. The guy at the auto parts store pulled a code of P0301, Cylinder 1 misfire detected. The suggested remedy was a new spark plug. That's not surprising, but I didn't think that was due until 120,000 miles. The car seemed to be running normally, without any problems that I could notice.

I called my mechanic, and he can't get me in until sometime next week. He suggested that I drive as little as possible until then, claiming I might damage a coil. I'm good with that, but I was miles from home and in the middle of doing things that had to be done, so I kept driving and running my errands.

Later that day, I saw that the light was off.

Did I magically cure the problem? Do I still need to get to the garage ASAP? Will I win the Powerball this weekend? What gives?

 

Gas cap was the first thing I checked. Haven't checked battery.