The rest of what OW says is that it is a mild winter rest of several weeks to a couple months but never to go dry for long. So since yours is mounted, I doubt you overwatered. They do like colder temps in winter too. I just got one of these a year ago and I kind of forgot I could have given it colder than I did, and drier. I hope mine does OK. Yours does look like a bit of moisture caused that yellow leaf since there are a couple black spots.