Apple Watch 8 Suddenly Overestimating Activity Calories and Flights Climbed

My Apple Watch 8 has suddenly started calculating an unusually high number of calories burned—about twice as much as usual. My heart rate is normal, and my activity level hasn’t changed.

I also noticed that the number of flights climbed has jumped from an average of 20 to around 200. When I checked the Compass app, I saw that my altitude is sometimes erratically jumping from 5 meters to 7,500 meters (and I’m definitely not climbing Everest every day!).

Does anyone know why this is happening and how I can fix it?