My 19 year old IR horse started acting strangely yesterday. He has was diagnosed with controlled IR. He's on a mineral balanced diet and chasteberry.  No medication. He's not foot sore. He lives on a track. He has access to a small amount of weeds, which he may pick at. He gets daily riding. Yesterday when I brought him in to ride, he was walking a bit wobbly. He kept stretching he neck out and couldn't hold it up as well as he normally does. I only rode him for a few minutes because it seemed like he was having trouble coordinating his body. For most of rest of the day he stood around sleeping. His appetite is good, but when I put the hay nets out, he seemed to have trouble pulling the hay through the holes. This morning he's alert and eating but still looks a bit uncoordinated.

He's been tested a couple of times for PPID, but it always comes back negative.

I remembered that people with diabetes can sometimes act drunk. So I started to wonder if this happens to horses too and what does it mean? Is there something I should give him? My local vets keep telling me there is nothing wrong with him. I got the controlled IR diagnoses from IR calculator when his blood work came back.
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Susan in BC 2020
https://ecir.groups.io/g/CaseHistory/files/Susan%20and%20Copper%20and%20Ella