They do get neurological issues sometimes and if that's the cause I'm not sure there's anything that can be done other than sensitive end-of-life care
BUT it is most important to rule out the completely treatable dental problems/middle ear infections that can also cause such symptoms. eg:
weight loss, drooling, and lower energy levels
spurs on back teeth that dig into the soft tissues of the mouth causing pain, or overgrown incisors which mean the mouth can't close properly, both make eating difficult which would explain all of the above. Reduced appetite for hay - which is hard work to chew and the grinding of this keeps those back teeth down - can itself lead to even more overgrowth.
Sometimes there can be ulcers in the mouth (sensitive tissues... maybe old age or a little too much fruit) or an abscess at the root of a tooth which causes pain when eating. I wouldn't be giving up just yet even though he's an older boy... his immune system might just be flagging a bit.
has some loss of balance,
Have they thought to try a combination of antibiotic and painkiller? This could address any potential middle ear infection which would cause dizziness and loss of balance. Putting the head up to reach the bottle might just be too much - a bowl in the meantime would help him avoid dehydration. If he actually is coming to the end of life something like the metacam/loxicom which we get prescribed here (usually twice a day) can help him be more comfortable.
If you can put your State in your location bar there might be other members nearby who have a vet recommendation - it's a bit of a long shot as the US is bigger than the UK... that much I do know!
I had a boy who was diagnosed with a neurological issue: started with a head tilt (which he arrived with), eventually he had to lean against the wall to move around or he just fell over, but he wasn't 'unwell' he was actually really cheerful and he
never stopped eating! He had to have a low bowl for food and water against the wall so he could lower his head while eating but he always looked like he was smiling, bless him, until the inevitable - because there was no cure.
Don't give up hope just yet
