my 27month old is so lethargic and out of sorts

[bigspender30]

For the past week he has been sleeping later in the morning ( usually a very early riser) and asking for bed at 4 in the afternoon. This is after napping for an hour at midday. Its so unlike him. He is usually swinging from the lights but he doesn't have a cold , no temperature or any visible signs of illness except the lethargy. Does this warrant a trip to the doctor? Help!

it can't help to get him checked out
maybe it is a virus or his back molars are coming through?

would the back molars cause this sort of lethargy? He doesn't seem to be knawing his hands much though like he usually does when teething.