A few weeks ago a customer returned a high quality watch because it was running very fast but when it reached me it was keeping time within a few seconds a day, after a prolonged test I sent it back. It then came back again with the same problem.
This time the watch was still running fast when it reach me and I was able to see that the two outer coils of the hairspring where "stuck" together, when freed the watch was again fine, keeping time to better than 5 seconds a day.
The cause of the problem was the hairspring becoming magnetised, almost certainly putting the watch too close to the customers iPad, hopefully the watch will be OK when degaussed - a tricky operation with a hairspring as it will vibrate with the degaussing field.
Don't get paranoid about it, but keep your watch away from computers, power-packs or anything else which might have a strong magnetic field.