My check engine light has been on for about 3 weeks. I scanned it immediately and got code P0141 (O2 sensor, Bank 1 Sensor 2). I haven't noticed any other changes in my car's driving other than maybe a slight decline in gas efficiency but that could be in my head since I know that can happen with a faulty O2 sensor.
I have an appt w a shop on Friday, but now the light is off. It turned off last night, and I've driven about two hours so far since and it's still off. I know the bulb isn't burnt bc it still flashes on when I start the car. What does it mean for the check engine light to just turn off like that?

98 Civic, 81k miles. Never given me any other problems before, except for muffler hair which required me to change the muffler out