Should I take my rabbit to the vet?

If he is acting strange and not eating well, you should definitely get him checked out. Rabbits are fragile and sensitive, even small signs could signal something very bad. Rabbits had to be good at hiding their illness or injury to survive in the wild; predators go for the weak. That's why rabbits instinctually hide it if something's up. Please take him to the vet, it's better safe than sorry. Good luck!

It's hard to give an answer without more detail. How long has he been going without eating? Did you recently change his diet? Is there any discharge coming from his nose? When you put your head near his body do you hear wheezing when he breaths?

If it's been more than 2 days since he's eaten, I would take him to a vet. Also, does he has diarrhea? This, known as wet tail, can be very detrimental to small animals and should be treated immediately.

Yes