Snake shed recently but seems about to shed again

[LtTawnyMadison]

Hi, my daughter's 9yo corn snake was usually shedding once a month (since we got him about a year ago) but then hadn't shed at all yet in 2020 until about 2 weeks ago. (We're going to start keeping a log). But it seems like he's already about to shed again. Last Sunday he didn't eat, and he hasn't come out for a few days now. He's under his warm-side hide and he looks very dull. I'm just not sure that he's actually getting ready to shed or if something else might be wrong, so I'm trying to find out whether we should be worried. The temp and humidity is OK, and when I checked on him he lifted his head and seemed alert.

One thing I just thought of -- last Sunday when my daughter tried to feed him she accidentally left the lid off. A couple of hours later we heard something fall and went to investigate, and very luckily saw him on a shelf of her bookcase. Now I'm hoping he didn't hurt himself somehow. He seemed fine at the time.