rabbit's teeth are overgrown, front and back. This happens due to various reasons- incorrect diet being the most common one. When these teeth grow too much they start eating up the healthy bone and cause localised swelling and infection which you now see as a swelling on his neck.
Needs surgical intervention. Abscess needs to be drained or excised, teeth will require multiple sessions of burring/trimming to achieve a normal occlusion. Severely infected and loose teeth might need to be removed.( I don't see any right now)
It a long process and you'll have to be supportive to you rabbit all throughout.
He's unable to chew and eat drools coming from his mouth and he is becoming week day by day
He needs multiple trimming to heal this problem.
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