I have to respectfully disagree NH93. If Audi007's snake is acting as described (half of the body is stiff like a stick and will not move), it sounds like he may be having some sort of neurological issue, a seizure or something. Maybe eating the big meal was a trigger? Even with the big meal in his stomach, going "stiff" is not normal. Audi007, can you provide any more information?
Is your entire tank 80F?
Has your snake ever shown any indication of this type of behaviour before?
Did he ingest any substrate along with the mouse?
Has he been eating/pooping normally prior to this?
As NH93 asked, can you provide a picture?
As she has already said, you need to be providing a proper heat gradient for digestion. This kind of behaviour would definitely indicate a vet visit, even if he does return to "normal" after a while (I would not wait to find out), you'd likely want to find out what caused it. Please keep us posted.