Hi everyone, it’s my first time posting here. I had my mare for 8 years (she was 16 when she suddenly passed) and never had any health issues besides uveitis in her left eye that left that eye blind. She had just got a yearly physical and vaccinations a little over a month before the incident. She was totally fine the night before, all of her food and hay was eaten as she was in her stall for the night.
 I got a call to come up to the stables urgently because she was having severe neurological symptoms. She was falling down, struggling to get up and holding her head to the side. She was interested in her breakfast but too uncoordinated to eat it and I quickly took it away. There were tons of marks on her mats where she would fall and try to get back up as well as the sand (she had a stall and long run). A vet was there in 20 minutes and originally thought it was severe EMP that came on instantly, which is usually not how that works as she had no prior symptoms and I’ve had a horse with it before so I know the ‘typical’ signs. She was flaring her lip a lot, signaling she was in pain, so she was given a max amount of banamine to help. 
I went and cold hosed her to try to calm her down. I need to add that she had no fever, no increased heart or lung sounds and peed and pooped fine during the ordeal. She went down while hosing and was groaning still in severe pain. But once she got up, her neurological signs pretty much vanished. She was walking relatively normally, held her head fine, and wasn’t falling randomly down. 
 Unfortunately, even after the pain medication she was still showing signs of severe pain. She would ease herself down and groan, and her breathing was becoming shallow. We even thought she stopped breathing at one point and unfortunately that’s when we made the call to euthanize her. The vet basically told us that she doesn’t know what happened and it’s such a hard pill to swallow after a perfectly healthy horse dies suddenly in two hours after being fine… the last key point of evidence is once she passed, blood was coming from her nose. I made the comment her gums looked pale while she was alive and I was blown off, even mentioning a rupture or possible aneurysm despite it taking a long time to kill her.
So knowledgeable horsey people, give me your thoughts on how my girl passed to help me sleep better at night 🤍