sleepy or sick or dying???

im very scared apologies for any typos. i found my rat in his cage sleeping where hs usually doesnt, so i checked on him and he was limp like a ragdoll. he's got plenty of fresh food and water, but hes just lethargic. his body feels and seems normal, his breathing is a little faster than usual but not by much- but he's letting me hold him. hes sleeping in my lap. hes never done any of this and hes just not being himself. he's quite old, 4 or 5 i want to say, but he was fine and active just a few days ago. he isnt caged with any other rats, as hes aggressive over living spaces, but hes been around my other rats for playtime and such and all of them are acting fine.

so sorry if this isnt the right place to ask im just very nervous and worries and if hes going to die in my arms or something i . want to know i guess. thank you in advance